Volume  I  MARCH,  1913  No.  2 


I 

A  Course  in  Physical  Nature  Study 

FOR  THE  E  L  E  M  E  NTARY  SCHOOL 


WM.  T.  SKILLING 


PUBLISHED  QUARTERLY  BY  THE  STATE  NORMAL  SCHOOL  OF  SAN  DIEGO 
SAN  DIEGO,  CALIFORNIA 


Application  made  for  entry  as  second  class  matter  at  the  Postoffice  at  San  Diego,  California 


Friend  Wm.  Richardson,  Superintendent  of  State  Printing 

SACRAMENTO,  CALIFORNIA 

1913 


..Or 

l'^ 

•  '  I  •  \  ■ 

INDEX. 

— —  C 

Page. 

The  Air  _ .• _  6 

The  Barometer _  6 

Gases  in  the  Air - 1 _  9 

Capillarity  _  10 

The  Solvent  Action  of  Water _  11 

Heat  and  Cold _  11 

Way  in  which  Heat  is  Made -  1 1 

How  Heat  is  Transferred _  12 

Heat  Currents  in  the  Air -  13 

Wind  _  13 

Examples  of  Radiation -  14 

Keeping  Heat  In  or  Out _  14 

Freezing  and  Thawing _  17 

Expansion  of  Water  in  Freezing _  17 

Artificial  Ice  -  18 

A  Study  of  Machinery _  19 

•  The  Eever  -  21 

The  Pulleys _  22 

The  Cog  Wheels - . _  22 

The  Belt  and  Belt  Wheels _  22 

The  Inclined  Plane -  22 

The  Screw _  23 

The  Windlass  -  23 

Eight  _  24 

The  Sources  of  Eight -  24 

Speed  - 1 -  24 

Reflection  _  24 

Diffusion  -  25 

Refraction  -  25 

Color  _  26 

Images  (Camera,  etc.) _  26 

Sound  _  27 

Vibrations  -  27 

How  Sound  Travels _  28 

The  Speaking  Tube -  30 

The  Megaphone  _  30 

The  Speed  of  Sound _  30 

Echo  -  30 


IV 


INDEX. 


Page. 

Magnetism  _  32 

Eeectricity  -  34 

The  Bell _ 2 _  35 

The  Push  Button _  36 

The  Telegraph  - ; -  36 

The  Electric  Eight -  38 

Frictional  Electricity  _  38 

Discussion  of  Other  Applications -  38 

Astronomy  _  41 

The  Solar  System -  41 

The  Sun _  44 

Day  and  Night -  46 

Difference  of  Temperature  in  Different  Zones -  48 

The  Planets  _  49 

The  Moon  _  50 

Eclipses  of  Sun  and  Moon -  51 

Comparison  of  the  Moon  with  the  Earth -  52 

The  Tides  _  53 

The  Stars _  55  • 

The  Constellations _  55 

Books  Suggested  for  Reference -  56 


INTRODUCTION. 


A  well  known  exponent  of  nature  study  defines  the  subject  as  being 
“a  simple  observational  study  of  common  things  and  processes.” 

The  work  outlined  in  this  bulletin  rigidly  excludes  abstract  scientific 
generalizations  and  complicated  apparatus,  and  is  therefor  simple.  It 
insists  upon  the  observational  method,  deals  with  the  common  things 
of  life,  and  finally,  lays  emphasis  upon  processes  as  well  as  things. 

The  course  comprised  here  is  not  a  general  nature-study  course,  but 
is  made  up  of  that  much  neglected  branch  of  the  subject  known  as 
physical  or  inorganic  nature  study.  Experience  has  proved  that  children 
of  the  upper  grammar  grades  take  a  more  vital  interest  in  the  processes 
of  inorganic  nature  than  they  do  in  the  old-fashioned  “object  lesson” 
or  in  work  which  is  exclusively  biological.  The  difficulty  of  adapting 
material  drawn  from  the  sciences  of  physics,  chemistry,  physical  geog¬ 
raphy,  and  astronomy,  is  considered  so  great  by  teachers  that  they 
are  tempted  to  content  themselves  with  the  more  objective  material 
supplied  by  botany  and  zoology.  A  study  of  flowers  and  butterflies 
may  suffice  in  the  primary  grades,  but  when  the  child’s  “what”  changes 
to  “why,”  we  must  put  him  into  contact  with  some  of  the  easily 
demonstrated  lav/s  of  nature  and  let  him  feel  that  he  is  coming  into  a 
knowledge  of  the  forces  about  him. 

It  is  strongly  recommended  that  the  experiments  and  demonstrations 
suggested  here  be  not  neglected,  for  they  are  the  life  of  the  course.  A 
little  foresight  in  the  matter  of  preparation  and  a  very  little  expense  at 
certain  points  will  enable  any  enthusiastic  teacher  to  accomplish  all  the 
work  including  the  illustrative  material  outlined  in  the  bulletin. 

While  it  is  true  that  there  is  material  here  which  may  be  adapted  to 
any  grade  from  the  primary  to  the  high  school,  yet  it  is  not  advisable 
to  give  this  work  as  a  whole  below  the  sixth  grade,  and  the  seventh  or 
eighth  grade  is  preferable  for  it.  The  time  required  to  accomplish  it  is 
at  least  one  hundred  minutes  a  week  for  one  year. 


Digitized  by  the  Internet  Archive 
in  2018  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/courseinphysicalOOskil 


THE  AIR, 


A  study  of  this  substance  so  near  to  us  and  yet  so  little  understood 
by  children  will  serve  as  a  good  starting  point  in  that  large  group  of 
subjects  classified  as  Natural  Science. 

To  establish  in  the  minds  of  the  pupils  the  reality  of  this  intangible 
thing  may  very  well  be  the  first  subject  to  achieve. 

Have  the  children  fan  the  air  into  their  faces  with  a  book  or  paper. 

Show  by  holding  the  finger  over  the  outlet  of  a  bicycle  pump  that  the 
air  has  force  to  prevent  the  piston  from  being  pushed  into  the  barrel 
of  the  pump. 

Show  pressure  of  air,  using  a  popgun. 

Teach  that  wind  is  air  in  motion. 

That  air  is  in  the  earth  as  well  as  above  it  may  be  shown  by  dropping 
a  large  clod  into  a  vessel  of  water  when  air  bubbles  will  be  seen  to  rise 
from  the  clod. 

That  air  is  in  water  also  is  shown  by  heating  some  water.  Bubbles 
of  dissolved  air  will  form  and  escape  long  before  the  water  is  hot 
enough  for  steam  bubbles  to  form. 

Fishes  breathe  this  air  and  would  smother  in  l.ioiled  water. 

The  pressure  of  air  is  a  property  requiring  demonstration. 

Completely  fill  a  glass  or  bottle  with  water.  Lay  over  the  mouth  of 
the  vessel  a  small  piece  of  paper  and  quickly  invert.  The  pressure  of 
the  air  against  the  paper  is  greater  than  the  weight  of  the  water  which 
is  held  up.  Remove  the  paper  and  notice  that  as  bubbles  of  air  go  in, 
the  water  goes  out. 

Pressure  may  be  shown  in  a  somewhat  similar  way  by  running  a 
string  with  a  knot  on  the  end  through  a  circular  piece  of  leather  (or 
rubber)  and  trying  to  pull  the  leather  from  a  smooth  wet  surface. 
Unless  the  air  gets  under  the  leather,  it  can  not  be  raised  easily  on 
account  of  air  pressure  on  top  of  it.  Emphasize  that  the  force  holding 
it  down  is  pressure,  not  suction.  Suction  is  not  a  force  at  all. 

Star  fish  and  other  sea  animals  cling  to  the  rocks  by  suction,  but 
flies,  contrary  to  the  conimon  opinion,  do  not. 

The  Barometer. — This  instrument  which  depends  upon  air  pres¬ 
sure  is  very  useful  in  making  clear  some  principles  of  the  action  of  air. 

Explain  the  barometer,  and  teach  that  it  reads  higher  in  low  places 
because  of  the  greater  weight  of  the  air  above  it. 

Illustrate  the  weight  of  the  air  by  piling  up  several  books;  place  the 


8 


PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCHOOL. 


hand  beneath  them  all,  then  place  the  hand  under  a  few  of  them  at 
the  top  of  the  pile. 

At  sea  level  the  air  is  heavy  enough  to  hold  the  mercury  in  the  tube 
of  the  barometer  about  30  inches  high.  Nine  hundred  feet  higher  the 
air  holds  the  mercury  about  29  inches  high. 

If  the  school  has  a  barometer,  take  it  to  the  highest  and  the  lowest 
places  accessible,  and  notice  the  exact  difference  in  reading. 

Calculate  the  difference  in  elevation  between  the  two  places,  by  means 
of  this  difference  in  readings. 


Fig.  1. — A  home-made  barometer  is  an 
instructive  piece  of  apparatus. 


A  barometer  can  be  made  very  easily  by  sealing  a  glass  tube  rather 
smaller  than  a  lead  pencil  and  about  35  inches  long.  To  seal,  hold  in  a 
gas  or  lamp  flame  about  two  inches  from  one  end  and  when  the  glass 
is  soft  pull  off  the  end.  This  leaves  the  tube  closed  at  that  end.  Fill 
the  tube  with  mercury,  using  a  medicine  dropper,  and  invert  it,  while 
holding  the  finger  over  the  end,  in  a  small  vaseline  bottle  of  mercury. 
The  tube  must  be  entirely  full  before  inverting  so  that  no  air  will  be 
left  in  it.  About  half  a  pound  of  mercury  is  necessary. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


9 


To  invert  the  tube  full  of  mercury  in  a  small  mouthed  bottle  into 
which  the  finger  will  not  go,  cover  the  end  of  the  tube  with  a  wide 
elastic  baud  drawn  tight  to  prevent  the  mercury  from  falling  out  of  the 
tube.  The  rubber  baud  may  be  removed  as  soon  as  the  open  end  of  the 
tube  is  below  the  surface  of  the  mercury  in  the  bottle. 

The  bottle  and  tube  may  be  securely  fastened  now  with  string  or  wire 
to  a  board,  the  string  to  be  passed  through  holes  bored  in  it.  A  block  for 
support  may  be  nailed  just  below  the  bottle.  A  yardstick  can  be  slipped 
in  behind  the  tube  as  a  scale.  Set  its  zero  end  level  with  the  mercury 
surface  in  the  cup. 

During  the  season  of  rains  the  children  should  become  familiar  with 
the  use  of  the  barometer,  recording  the  readings  with  changing  weather. 

Gases  in  the  Air. — Pupils  should  know  something  of  the  various 
constituents  of  the  air  and  the  uses  of  each.  A  few  simple  experiments 
are  necessary  to  make  these  invisible  substances  realities  to  them. 

(a.)  Water  vapor.  If  ice  is  obtainable,  show  the  pressure  of  moisture 
in  the  atmosphere  by  the  “sweating”  of  a  cold  water  pitcher.  Let  pupils 
report  evidences  they  have  observed,  as  the  formation  of  dew,  fog, 
rain,  etc.,  and  the  evaporation  of  water  into  the  air. 

{h)  Oxygen.  One  fifth  of  the  air  is  oxygen.  Plants  as  well  as 
animals  would  die  without  it.  Fire  must  have  it  to  burn  at  all.  It  is 
that  which  rusts  iron  and  brings  about  decay.  The  easiest  way  to 
make  oxygen  for  class  experiments  is  to  sprinkle  a  little  sodium  peroxide 
(from  the  drug  store)  upon  water  contained  in  the  bottom  of  a  jar 
or  tumbler.  Oxygen  is  rapidly  set  free  from  the  chemical  and  fills  the 
vessel,  which  should  be  loosely  covered. 

Hold  a  glowing  splinter  over  the  vessel  and  see  it  burst  into  flame. 
Fasten  a  small  splinter  to  the  end  of  a  raveled  picture  wire.  Light 
the  wood  and  quickly  introduce  into  a  jar  of  oxygen.  The  wire  takes 
fire  and  burns.  Discuss  conditions  if  air  were  all  oxygen. 

(c)  Carbon  dioxide.  This  gas  though  forming  but  a  small  proportion 
of  the  air  is  the  chief  food  of  all  vegetation,  being  absorbed  through 
the  leaves. 

The  gas  can  be  made  in  abundance  by  sprinkling  cooking  soda  into 
a  jar  containing  a  little  vinegar  or  other  acid.  Nothing  will  burn  in  it. 
Try  a  match  or  candle.  It  is  heavy  and  can  be  poured  from  a  jar  into 
a  tumbler.  It  will  make  lime  water  milky  and  is  usually  detected  in 
this  way.  Pour  some  into  a  glass  of  lime  water  and  shake  it  up.  The 
water  becomes  white.  Blow  the  breath,  which  contains  much  of  it, 
through  a  straw  or  tube  into  lime  water.  Let  a  glass  of  lime  water 
stand  for  several  days  exposed  to  the  air;  a  white  crust  will  form 
showing  presence  of  carbon  dioxide  in  the  air. 


10 


PHYSICAI,  NATURE  STUDY,  ElEMENTARY  SCHOOE. 


CAPILLARITY. 

Capillarity  is  the  rise  of  liquids  in  tubes. 

Select  several  tubes  of  different  internal  diameter  and  dip  them  into 
water.  The  water  rises  in  all  of  them,  but  in  the  smaller  ones  it  rises 
much  higher.  It  has  been  found  by  careful  measurement  that  the  height 
of  the  water  varies  inversely  as  the  diameter  of  the  tubes. 

Notice  the  shape  of  the  surface  inside  the  tube.  Draw  a  picture  of 
the  tube  and  its  contents.  Is  the  surface  concave  or  convex? 

Put  the  tubes  in  alcohol.  This  does  not  rise  so  high.  All  liquids 
differ  from  one  another  in  respect  to  capillarity. 

Put  the  corner  of  a  lump  of  sugar  into  water.  Soon  the  whole  lump 
is  wet.  The  pores  in  the  lump  act  as  capillary  tubes.  Do  the  same 
with  a  clod  of  earth.  Hang  one  end  of  a  strip  of  blotting  paper  into 
ink.  Put  one  end  of  a  lamp  wick  into  a  glass  full  of  water  and  let 
the  other  end  hang  in  an  empty  glass.  Allow  to  stand  until  the  two 
glasses  are  about  equally  full. 

Fill  two  cans  or  tumblers  with  mud.  Weigh  tliem  carefully  and  adjust 
them  so  that  they  both  weigh  the  same.  Now  set  them  in  a  sunny, 
airy  place,  and  as  soon  as  the  surface  begins  to  dry  out,  scratch  up  the 
surface  of  one  of  them  with  a  match  or  toothpick,  but  let  that  of  the 
other  bake  hard  without  being  disturbed.  Every  day  set  them  on  oppo¬ 
site  pans  of  the  balance  and  notice  that  the  one  with  a  hard  surface  is 
becoming  lighter  than  the  other.  Also  weigh  them  frequently,  seeing 
how  much  water  each  is  losing.  The  experiment  illustrates  the  fact  that 
cultivating  the  soil  after  rain  or  irrigation  tends  to  keep  the  water  in ; 
but  allowing  the  ground  to  bake  on  top  causes  it  to  dry  out.  Why 
is  this? 

If  the  ground  becomes  hard  and  baked,  the  pores  act  as  capillary 
tubes  to  draw  the  water  to  the  surface  where  it  can  be  evaporated. 
But  if  the  surface  is  made  loose  by  cultivation,  the  pores  are  made  so 
large  that  they  cannot  draw  the  water  up  from  below,  and  so  it  never 
comes  up  where  the  sun  and  wind  can  evaporate  it. 

Such  a  covering  of  fine  dirt  is  called  by  farmers  a  “dust  mulch.”  A 
mulch  of  straw  or  leaves  has  the  same  effect,  namely,  to  keep  the  water 
from  coming  up  to  be  evaporated. 


SAN  DIEGO  STATE  NORMAE  SCHOOE. 


11 


THE  SOLVENT  ACTION  OF  WATER. 

Dissolve  salt,  sugar,  alum,  etc.,  in  water.  Use  an  excess  of  the  solid 
and  stir  well.  The  result  is  a  saturated  solution.  (Give  definition  of 
a  saturated  solution.) 

Pour  off  the  clear  liquid  from  each  solution  and  heat  it.  Add  more 
of  the  solid  little  by  little.  This  shows  that  hot  water  is  a  better  solvent 
than  cold. 

Pour  into  an  evaporating  dish  (a  tin  cup),  and  boil  off  the  water. 
Notice  that  the  solid  is  left  behind  unchanged. 

Evaporate  to  dryness  in  a  clean  white  evaporating  dish  (or  tin  cup) 
some  hydrant  water.  It  also  leaves  some  sediment,  showing  that  it  is 
not  pure.  Why  is  it  not  pure?  Talk  of  the  different  substances  in  the 
earth  over  and  through  which  the  water  has  flowed  before  coming  to 
the  hydrant. 

Other  Solvents.  There  are  some  things  which  water  will  not  dissolve 
but  other  liquids  will.  Put  a  lump  of  butter  into  water  and  another 
into  gasoline  or  ether.  Gasoline  and  ether  are  used  to  remove  grease 
spots  from  cloth. 

To  Shezv  that  Gases  are  Dissolved  in  Water.  Put  water  into  a  test 
tube  and  heat  gradually.  Bubbles  can  be  seen  coming  off  before  it  begins 
really  to  boil.  These  bubbles  are  air. 

“Soda  water”  contains  a  gas  (CO^)  dissolved  in  it  in  great  quantities 
by  means  of  -pressure.  When  the  pressure  is  removed,  the  liquid 
effervesces. 

HEAT  AND  COED. 

As  an  easy  transition  from  air  to  heat  discuss  the  effects  of  heat  upon 
air  and  other  gases.  Heat  expands  everything,  but  gases  most  of  all. 

Put  a  one-hole  stopper,  through  which  passes  a  glass  tube,  into  a 
bottle.  Dip  the  end  of  the  tube  into  water.  Nothing  happens.  Warm 
the  bottle  with  your  hands.  Bubbles  escape.  Cool  the  bottle  with  water. 
The  air  contracts  and  water  rises  into  the  bottle. 

Give  an  oral  and  a  written  account  of  all  that  was  done,  with  reasons 
for  each  step. 

Heat  the  bottle  with  a  match  or  candle.  The  effects  are  magnified. 
Hold  it  in  the  sun  or  near  a  fire. 

Ways  in  Which  Heat  is  Developed. —  (a)  By  means  of  friction. 
Have  the  children  rub  their  hands  vigorously  together. 

Rub  a  coin  hard  for  some  time  upon  the  floor  or  a  table,  and  pass  to 
several  pupils  to  report  on  its  heat. 


12 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL- 


File  a  nail  and  pass  it  around  the  class. 

Have  the  pupils  report  other  instances  of  heat  caused  by  friction. 

Why  is  machinery  oiled? 

(b)  By  chemical  action.  Pour  water  over  a  cup  of  quick  lime. 

Teach  that  all  chemical  action  produces  heat,  but  that  the  degree  of 

heat  produced  varies  with  the  substances  used. 

Mention  spontaneous  combustion  of  oily  rags. 

(c)  By  hrc.  Explain  that  fire  is  rapid  chemical  action,  and  that 
the  burning  of  some  fuels  produces  more  heat  than  is  the  case  with  • 
others.  Discuss  different  fuels  used  to  produce  heat  and  light. 

Teach  that  fire  is  made  by  the  uniting  of  a  fuel  with  the  air.  Also 
that  the  new  substances  produced  are  carbon  dioxide  and  water. 

Hold  a  thick  glass  jar  over  a  flame  to  show  the  moisture. 

How  Heat  is  Transferred. — Heat  is  transferred  from  one  place 
to  another  in  three  ways  :  Conduction,  convection  currents,  and  radia¬ 
tion,  or  shining. 

Hold  a  wire  in  the  flame  of  an  alcohol  lamp.  The  heat  of  the 
flame  runs  slowly  up  the  wire.  This  is  conduction. 

Put  some  sawdust  in  a  test  tube  of  water  and  heat  at  the  bottom. 
The  water  when  warmed  rises,  as  can  be  seen  by  the  movement  of 
the  sawdust,  and  heat  is  carried  to  the  top.  This  is  a  convection  cur¬ 
rent.  Have  pupils  draw  diagrams  showing  upward  and  downward 
currents  by  arrows. 

Hold  the  hand  beside  a  flame,  not  over  it.  The  heat  shines,  or 
radiates,  and  warms  the  hand.  This  is  radiation. 

Hold  the  hand  over  the  flame.  The  hot  air  rises  to  the  hand. 

This  is  a  convection  current. 

To  Show  that  Some  Things  Conduct  Heat  Better  than  Others.  Hold 
several  wires  of  different  metals  (iron,  brass,  copper)  in  an  alcohol 
flame.  Which  becomes  hot  farthest  from  the  flame?  Which  is  the 
best  conductor?  (Copper). 

Hold  one  edge  of  a  silver  coin  in  a  flame.  See  how  very  quickly 
heat  is  conducted  to  the  farther  edge.  Silver  is  the  best  of  con¬ 
ductors.  Select  a  piece  of  any  other  metal  similar  in  size  to  the 
silver  coin  {e.g.,  an  iron  washer).  Repeat  the  test  and  note  the 

difference. 

Non-metals  are  all  poor  conductors  of  heat.  Hold  broken  pieces 

of  glass,  pottery,  a  glass  tube,  a  stick,  a  stone,  a  clod,  in  a  flame. 

They  all  conduct  very  badly,  but  some  better  than  others, — stone  better 
than  wood,  for  example. 


SAN  DII:G0  state;  NORMAIv  school. 


13 


In  Alaska  and  other  cold  countries  stone  can  not  well  be  used  for 
building  houses,  for  it  conducts  the  heat  from  within  to  the  outside  so 
fast  that  it  is  difficult  to  keep  the  houses  warm.  A  wooden  house 
is  warmer,  for  wood  is  a  poor  conductor. 

To  Shozv  that  Water  is  Heated  by  Conveetion,  not  by  Conduetion. 
Heat  near  the  top  a  test  tube  filled  with  water.  The  bottom  remains 
cool,  for  water  is  a  poor  conductor,  and  the  warm  water  at  the  top, 
being  lighter  than  the  cold  water  at  the  bottom,  cannot  sink.  When 
the  flame  is  applied  below,  the  water  rises  as  fast  as  it  becomes  heated, 
and  so  the  whole  is  warmed. 

Heat  Currents  (Convection  Currents)  in  the  Air. — Strike  a  match. 
The  flame  rises.  Why  does  it  do  so?  The  flame  is  made  of  heated 
gases  in  which  are  floating  red-hot  solid  particles  which  give  it  its 
brightness  and  color.  These  gases  being  so  hot  are  very  light — less 
than  half  as  heavy  as  the  surrounding  air,  and  for  that  reason  they 
rise,  just  as  light  cork  would  rise  in  water  which  is  so  much  heavier 
than  it  is. 

Hold  a  large  glass  tube  or  a  tall  lamp  chimney  a  few  inches  above 
a  candle  or  alcohol  flame  so  that  the  column  of  air  in  the  tube  becomes 
heated.  Let  loose  small  fluffy  bits  of  cotton  in  the  lower  end  of  the 
tube.  These  are  carried  up,  often  to  the  ceiling.  There  is  no 
upward  motion  within  the  tube  until  the  air  there  becomes  heated  and 
so  is  made  lighter  than  the  outside  air. 

The  longer  the  tube  is  the  greater  the  force  of  the  upward  move¬ 
ment,  for  the  s'ame  reason  that  the  larger  a  piece  of  cork,  the  harder 
it  is  to  hold  it  down  in  water. 

The  draught  in  a  chimney  or  stovepipe  is  caused  by  the  air  within  it 
becoming  heated  and  therefore  lighter.  The  higher  the  chimney  the 
better  the  draught.  Smokestacks  on  locomotives  used  to  be  made 
high,  but  now  air  is  forced  through  the  fire  box  and  the  smokestack 
does  not  need  to  be  so  high. 

An  easy  and  striking  demonstration  of  the  fact  that  heated  air  rises 
made  be  made  by  heating  a  flat  iron  or  other  piece  of  metal  and  then 
holding  it  in  the  sunshine  at  a  window.  Where  the  sunlight,  after 
passing  the  metal,  falls  upon  the  floor  or  a  wall  or  a  large  white 
paper  held  several  feet  from  the  iron  the  rapid  upward  movement  of 
the  heated  air  is  convincingly  shown. 

Wind. — Some  winds,  not  all,  are  the  result  of  heat  and  cold. 
Just  as  a  fire  makes  a  movement  in  the  atmosphere  around  it  and  in 
the  chimney  above  it,  so  the  heat  of  the  sun  may  produce  air  currents 
which  are  called  winds. 


14 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


A  good  example  of  this  is  the  “sea  breeze.”  During  the  daytime, 
especially  in  summer,  the  land  becomes  warmer  than  the  ocean ;  so 
the  warm  air  over  the  land  rises,  being  crowded  up  by  the  cooler 
air  from  the  ocean  which  rushes  in  often  at  the  rate  of  eight  or  ten 
miles  an  hour,  forming  a  “sea  breeze.”  At  night  the  land  quickly 
cools  down  until  it  is  no  warmer  than  the  sea,  and  then  the  wind 
ceases  to  blow. 

Sometimes,  especially  in  winter,  the  land  at  night  becomes  much 
colder  than  the  sea,  and  so  during  the  night  the  wind  blows  to  the 
ocean.  This  is  called  a  “land  breeze.” 

At  the  equator  the  air  is  heated  by  the  tropical  sun,  and  thus  becom¬ 
ing  lighter  than  the  air  on  either  side  of  the  equator,  it  is  crowded 
upward  by  the  inrush  of  this  air  from  the  north  and  from  the  south. 
These  two  currents  are  called  Trade  Winds,  because  they  are  so 
constant  that  trading  vessels  can  take  advantage  of  them. 

Examples  of  Radiation. — Hold  a  book  or  piece  of  pasteboard 
between  the  hand  and  a  fire.  Remove  the  screen  suddenly  and  notice 
how  quickly  the  heat  reaches  the  hand.  Radiation  is  almost  instanta¬ 
neous.  The  heat  of  the  sun  reaches  us  by  radiation.  It  comes  at  the 
rate  of  186,000  miles  a  second,  reaching  the  earth  in  about  eight 
minutes  (500  seconds)  after  leaving  the  sun.  (Divide  93,000,000,  the 
distance  in  miles  to  the  sun,  by  186,000,  to  get  this  figure.) 

Hold  an  electric  light  bulb  in  the  hand  and  turn  on  the  light.  The 
hand  instantly  feels  the  warmth.  It  feels  as  if  the  globe  were  warm, 
but  it  is  not,  as  may  be  seen  by  turning  off  the  light  before  there  has 
been  time  for  the  heat  to  be  conducted  through  the  glass.  ( If  an 
electric  lamp  cannot  be  had,  use  a  coal  oil  lamp,  turning  it  up  and 
down.) 

Keeping  Heat  In  or  Out. — Why  are  some  garments  warm  and 
others  cool? 

When  we  speak  of  dressing  in  warm  clothing  to  keep  out  the  cold, 
we  mean  dressing  in  clothing  which  is  a  poor  conductor  of  heat  and 
so  prevents  rapid  loss  of  heat  from  the  body.  It  keeps  the  heat  in ; 
it  does  not  keep  the  cold  air  out.  Cold  is  nothing  but  the  absence  of 
heat,  just  as  darkness  is  simply  the  absence  of  light. 

The  body  is  always  warmer  than  the  air  except  on  extremely  hot 
days  ;  so  to  keep  warm  we  must  keep  the  heat  in,  and  to  keep  cool  we 
must  dress  so  as  to  let  the  heat  of  the  body  escape  easily. 

Woolen  cloth  is  a  poor  conductor  and  therefore  keeps  the  heat  in. 
Cotton  cloth  is  a  better  conductor  and  lets  the  heat  escape  more 
easily  and  rapidly. 


SAN  DIEGO  STATE  NORMAE  SCHOOL. 


15 


Effect  of  Color  in  Clothing.  So  far  we  have  spoken  only  of  loss 
of  heat  by  conduction.  But  when  we  are  out  in  the  hot  sunshine,  we 
need  to  be  protected  from  radiant  heat.  For  this,  color  is  of  more 
importance  than  material. 

Lay  two  thermometers  on  a  board  and  cover  one  with  a  black  cloth 
and  the  other  with  a  white  cloth  of  the  same  texture  and  thickness. 
Black  and  white  paste1)oard  may  be  used. 

The  one  under  the  lilack  cloth  will  run  up  faster  than  the  other, 
for  black  absorbs  radiant  heat  better  than  white.  For  this  reason 
light-colored  clothing  is  a  better  protection  from  the  sun’s  heat  than 
dark. 

A  black  hat,  even  black  straw,  is  a  poor  protection  against  the 
intense  heat  of  the  summer  sun. 

Red  is  almost  equal  to  black  as  a  heat  absorber. 

Building  so  as  to  Keep  Heat  In  or  Out.  To  have  a  house  warm  in 
winter  it  must  be  built  so  as  to  keep  in  the  artificial  heat.  To  have  it 
cool  in  summer  it  must  be  built  so  as  to  keep  out  the  sun’s  heat. 

Air  is  a  good  non-conductor  of  heat.  For  this  reason  a  "dead-air 
chamber”  is  left  in  the  walls  of  buildings  to  "keep  out  the  cold,”  or 
rather,  to  keep  in  the  heat.  The  ^ittic  of  a  house  also  acts  as  a  “dead- 
air  chamber,”  and  keeps  the  heat  within  from  escaping  as  well  as  the 
sun’s  heat  on  the  roof  from  being  conducted  through  the  interior. 
The  house  in  this  way  is  kept  cool  in  summer  and  warm  in  winter. 
Why? 

A  metal  roof  is  hot  in  summer  and  cold  in  winter  because  metal  is 
a  good  conductor. 

Ice  houses.  To  keep  ice  from  melting  it  is,  of  course,  necessary  to 
keep  out  the  external  heat.  This  is  accomplished  mainly  by  dead-air 
chambers.  But  an  empty  chamber  is  not  sufficient  for  this,  because, 
although  heat  would  not  be  conducted  across  the  empty  space,  still  it 
would  be  carried  across  by  convection  currents.  The  chamber  is 
packed  full  of  some  fibrous  non-conducting  substance  which  will 
entangle  the  air  in  its  meshes  and  prevent  convection  currents.  "Glass 
wool”  and  fibrous  asbestos  are  used  for  this  purpose. 

Why  is  fur  so  warm?  Fur  is  an  exceedingly  fine  hair.  Not  only 
are  the  fibers  fine,  but  they  are  set  close  together  so  that  the  air 
spaces  between  them  are  very  small.  The  air  is  entangled  in  these 
small  spaces  and  cannot  flow  in  convection  currents  freely  back  and 
forth  as  it  can  through  coarse  hair.  It  is  this  entangled  air  which 
prevents  the  heat  of  the  body  from  escaping. 


16 


PHYSICAL  nature  study,  ELEMENTARY  SCHOOL. 


All  animals  of  frigid  regions  possess  fine  fur,  while  those  of  tropical 
regions  have  hair  instead. 

Feathers,  like  fur,  are  very  warm,  and  for  the  same  reason. 

Wool  and  woolen  cloth  are  much  warmer  than  cotton,  partly  because 
the  fibers,  being  finer  and  closer  together,  prevent  free  circulation  of 
air,  and  partly  because  the  fibres  of  wool  are  themselves  poorer  con¬ 
ductors  than  those  of  cotton. 


Fig.  2. — A  thermos  bottle.  A  vacuum 
prevents  loss  of  heat  either  by  conduc¬ 
tion  or  convection  currents. 


The  very  liest  non-conductor  is  a  perfect  vacuum.  It  is  used  in 
keeping  the  heat  from  liquid  air  and  other  liquid  gases.  It  is  also 
used  to  keep  ordinary  liquids  either  hot  or  cold.  See  Fig.  2. 

The  liquid  in  question  is  put  into  a  bottle  which  has  a  double  wall, 
the  air  from  the  chamber  between  the  walls  having  been  removed  as 
completely  as  possible. 


SAN  DIEGO  STATE  NOR  MAE  SCHOOE. 


17 


Such  a  vessel  is  called  a  thermos  bottle  and  is  coming  into  very 
common  use.  Secure  one  if  possilile  for  experiments  in  keeping  ice 
water  cold  and  hot  water  warm. 

Can  heat  pass  1)y  convection  through  a  vacuum? 

A  vacuum  has  no  effect  upon  the  passage  of  radiant  heat,  1)ut  this 
would  be  slight,  and  to  make  it  less  the  outside  of  a  thermos  bottle  is 
silvered  to  reflect  back  the  heat  and  prevent  its  entering  the  outer 
covering. 

Freezing  and  Thawing. —  Temperature  of  freezing.  Stir  a  vessel 
of  water  with  a  thermometer  and  add  ice  till  the  temperature  falls  as 
low  as  it  will.  This  is  the  temperature  of  melting  ice.  It  is  0°  C.  or 
32°  F.  Ice  melts  and  water  freezes  at  this  temperature. 

Freezing  Mixtures.  Mix  salt  and  crushed  ice  in  a  cup  and  put 
the  mixture  into  a  test  tube  of  water.  Stir  the  ice,  and  the  water  in 
the  test  tube  will  freeze. 

Take  the  temperature  of  the  mixture  of  ice  and  water  with  a 
thermometer. 

Why  does  salt  mixed  with  ice  make  the  mixture  so  much  colder? 

Before  answering  this  question  lay  some  salt  (in  lumps)  on  a  cake  of 
ice  and  notice  how  much  faster  the  ice  melts  under  and  around  each 
lump  than  it  does  elsewhere. 

When  ice  melts  it  takes  the  heat  which  is  used  in  melting  it  from 
its  surroundings.  This  heat  may  be  taken  from  the  air  or  from  any¬ 
thing  near  the  ice.  If  a  thermometer  is  put  into  the  mixture  of  ice 
and  salt,  heat  is  taken  from  the  thermometer  itself,  and  it  falls. 

The  faster  the  ice  melts,  the  faster  heat  is  removed  from  its  sur¬ 
roundings. 

When  cream  in  a  can  is  put  into  the  mixture,  the  heat  is  rapidly 
taken  from  the  cream  by  the  melting  ice,  and  the  cream  freezes  as 
did  the  water  in  the  test  tube  in  the  above  experiment. 

Expansion  of  Water  in  Freezing. — Fill  a  test  tube  with  water  and 
insert  in  it  a  one-hole  stopper  through  which  runs  a  glass  tube.  See 
that  no  air  bubbles  are  left  in  the  test  tube.  Immerse  this  tube  in 
a  freezing  mixture  of  ice  and  salt.  As  soon  as  crystals  of  ice  begin 
to  form  in  the  test  tube,  the  water  begins  to  rise,  showing  expansion. 

After  much  of  the  water  is  frozen,  warm  the  test  tube  in  a  flame 
or  in  the  hands,  and  as  the  ice  disappears  the  water  falls,  showing 
contraction. 

The  water  really  begins  to  expand  4°  C.  above  the  freezing  point,  for 
then,  no  doubt,  the  molecules  of  water  begin  to  arrange  themselves 


18 


PHYSICAIv  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


in  crystalline  form,  though  the  water  does  not  become  solid  until 

zero  is  reached. 

This  CNpaiLsion  of  water  on  freezing  is  a  remarkable  exception  to 
the  rule  in  nature.  Almost  all  substances  when  melted  occupy  more 
space  than  when  solid. 

]\'[elt  a  cupful  of  paraffine  and  then  set  it  in  cold  water  to  hasten 

its  cooling,  and  notice  the  great  contraction  as  it  solidifies. 

Think  what  the  result  would  be  if  water  also  contracted  on  solidify¬ 
ing  to  ice.  Tt  would  become  heavier  than  water  instead  of  lighter  as 
ice  actually  is,  and  would  sink  as  fast  as  formed.  This  would  allow 
more  ice  to  form  on  top  which  in  turn  would  sink,  and  this  process 
would  go  on  until  the  lake  or  river  was  full  of  ice.  All  the  fish  would 
he  killed,  and  even  the  deepest  lakes  would  soon  become  solid  ice 

which  could  thaw  only  a  few  feet  deep  even  in  summer  time. 

There  is  one  other  substance  which  like  water  expands  on  solidify¬ 
ing.  This  is  bismuth.  Bismuth  is  a  metal  which  easily  alloys  with 
other  metals.  Type-metal  is  an  alloy  of  lead,  bismuth,  and  antimony. 
Bismuth  is  used  in  order  to  make  the  letter  expand  and  fill  the  mold  in 
which  it  is  made.  Any  metal  other  than  bismuth  would  shrink  away 
from  the  mold  on  cooling  and  so  make  an  imperfect  letter. 

Bismuth  expands  1/32  of  its  volume  on  solidifying;  ice  1/11. 

Artificial  Ice. — Ice  is  usually  made  by  the  rapid  evaporation  of 
some  liquid  which  evaporates  easily. 

Pour  a  little  ether,  or  carbon-bisulphide,  or  alcohol,  or  gasoline  on 
the  hand  and  blow  upon  it.  It  feels  very  cold,  for  in  order  to  be 
coiu'erted  into  vapor,  it  takes  heat  from  the  hand.  The  faster  it  can 
be  made  to  evaporate,  the  more  rapidly  it  takes  heat  from  the  sur¬ 
roundings  and  the  colder  they  feel. 

The  above  liquids  do  not  evaporate  rapidly  enough  to  make  ice, 
but  there  are  liquids  that  do.  Liquid  ammonia  (not  a  water  solution 
of  ammonia,  but  the  gas  compressed  to  a  liquid)  is  the  liquid  usually 
employed.  The  pressure  necessary  to  keep  it  in  the  form  of  a  liquid 
is  quickly  removed  and  it  evaporates  so  rapidly  that  the  water  sur¬ 
rounding  it  is  frozen. 

Liquid  CO.,  is  also  used,  and  gives  a  much  lower  temperature 
than  can  be  obtained  with  liquid  ammonia. 

Liquid  air  evaporating  gives  a  still  lower  temperature,  but  liquid 
air  cannot  be  made  so  easily. 


SAN  DIEGO  state  NORMAE  SCHOOE. 


19 


A  STUDY  OF  MACHINERY. 


All  kinds  of  machinery  are  made  up  of  one  or  more  simple  machines. 
There  are  only  a  few  simple  machines  ;  the  lever,  the  pulley,  the  cog 
wheel,  the  belt  and  belt  wheel,  the  inclined  plane,  the  wedge,  the 
screw,  and  the  windlass  are  the  principal  kinds.  See  Fig.  3. 

Each  of  these  machines  should  lie  studied  according  to  the  follow¬ 
ing  plan  : 

( 1  )  Make  the  machine  in  question  and  demonstrate  its  action  before 
the  class. 


Fig.  3. — If  pupils  make  simple  diagrams  of  the  machines,  they  will  more  easily  under¬ 
understand  their  principles. 


(2)  Let  the  class  give  illustrations  of  as  many  pieces  of  machiner\' 
as  possible  in  which  it  forms  a  part,  as  the  lever  seen  in  the  pump 
and  in  the  wheel  barrow. 

(3)  Give  the  “law”  of  this  machine, — that  is,  what  is  gained  by  using 
it.  For  example,  how  many  times  greater  is  the  load  to  be  lifted 
than  the  force  used  in  lifting  it.  Thus,  in  using  the  lever,  the  load 
lifted  is  always  as  many  times  the  power  used  as  the  power  arm  is 
times  the  length  of  the  load  arm. 

(4)  Work  a  few  simple  problems  to  illustrate  this  law. 


20 


PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCHOOL. 


The  following  are  suggestions  of  the  kind  of  problem  that  should 
be  used  during  the  discussion  of  each  of  the  machines  mentioned 
below  : 

The  Lever.  What  load  on  a  wheelbarrow  can  be  lifted  with  a 
force  of  fifty  pounds,  if  the  load  is  one  foot  from  the  wheel  and  the 
hands  four  feet?  (Ans.  200  lbs.) 

The  Pulleys.  If  five  cords  help  to  support  a  weight  being  drawn 
up  by  pulleys,  how  many  pounds  can  be  lifted  by  a  force  of  100 
pounds?  (Ans.  500  lbs.) 


Fig.  4. — Examples  of  simple  machines.  The  lever,  the  inclined  plane,  the  cog  wheels, 
the  screw,  the  belt  and  belt  wheels,  the  pulley  (two  pencils  with  a  cord  running  back  and 
forth  between  them),  and  the  windlass. 


The  Cog  Wheels.  If  the  small  wheel  of  an  egg  beater  has  eight 
cogs  and  the  large  wheel  forty,  how  many  times  will  the  beater  turn 
while  the  handle  goes  once  around?  (Ans.  5  times.) 

The  Belt  and  Belt  Wheels.  If  the  small  wheel  in  Fig.  3  is  3  inches 
in  diameter  and  the  large  wheel  18  inches,  how  many  times  will  the 
small  one  turn  for  each  revolution  of  the  large  one?  (x\ns.  6  times.) 

The  Inclined  Plane.  How  hard  will  horses  have  to  pull  to  draw  a 
wagon  up  a  hill  which  rises  10  feet  in  100  feet,  if  the  wagon  weighs 
2000  pounds?  (Ans.  200  lbs.) 


SAN  DIEGO  STATE  NORMAE  SCHOOL. 


21 


The  Screw.  If  the  hand  moves  100  inches  in  turning  a  jack  screw 
once  around  and  the  threads  are  I4  inch  apart,  how  many  pounds 
can  be  lifted  with  a  force  of  20  pounds?  (Ans.  8000  lbs.) 

The  Windlass.  With  an  axle  6  inches  in  diameter  and  a  crank  24 
inches  long,  how  heavy  a  w^eight  can  be  lifted  with  a  force  of  10 
pounds?  (Ans.  80  lbs.) 

The  Lever. — Make  a  lever  by  laying  a  yard  stick  across  some- 
object  which  will  serve  as  a  fulcrum,  and  demonstrate  that  a  heavy 
weight,  such  as  a  large  book,  may  be  lifted  by  using  a  very  slight 
force. 

Show  that  the  lever  may  be  used  in  three  different  ways ;  namely, 
by  putting  the  fulcrum,  the  weight,  or  the  power  between  the  other 
two.  These  ways  illustrate  levers  of  the  first,  the  second,  and  the 
third  class.  (See  Fig.  3.) 

The  class  should  give  as  examples  the  crowbar,  nut  crackers,  an 
ax  when  used  in  chopping,  the  claw  hammer,  scissors,  a  pump  handle,, 
sugar  tongs,  etc. 

Teach  the  law  of  the  lever  as  follows:  The  load  to  be  lifted  is  as 
many  times  the  power  necessary  to  lift  it  as  the  power  arm  is  times  the 
load  arm.  (In  all  three  kinds  of  lever,  the  arms  are  measured  from 
the  fulcrum.)  In  the  eighth  grade  teach  also  that  the  product  of 
the  load  arm  times  the  load  is  .equal  to  the  product  of  the  power 
arm  times  the  power.  Also,  if  proportion  has  been  studied,  that  the 
load  arm  is  to  the  power  arm  as  the  power  is  to  the  load. 

Find  by  calculation  the  weight  of  a  number  of  articles  as  follows : 
Support  a  yardstick  at  the  middle  by  means  of  a  string  run  through 
a  small  hole.  Hang  from  any  point  on  one  arm  by  means  of  a  string 
some  known  weight,  say  a  pound,  and  on  the  other  arm  attach  similarly 
some  unknown  weight.  Slip  the  latter  along  until  it  balances,  and 
then  noticing  its  distance  from  the  point  of  support,  calculate  its 
weight,  using  one  of  the  three  statements  of  the  law  of  the  lever  as 
given  above. 

If  this  work  be  introduced  below  the  eighth  grade,  require  of  the 
pupils  only  an  approximate  answer  by  making  a  mental  estimate. 

Hang  a  bucket  on  a  pole  between  two  pupils,  and  have  them  estimate 
or  calculate  the  proportion  of  the  weight  that  each  lifts  with  the  load 
at  various  points. 


22 


PHYSTCAI,  NATURE  STUDY,  EEEMENTARY  SCHOOE- 


The  Pulleys  (Block  and  Tackle). — To  represent  the  block  and 
tackle  in  the  simplest  possible  manner,  place  two  lead  pencils  parallel 
about  a  foot  apart.  Tie  a  thread  to  one,  and  pass  it  back  and  forth 
between  the  two  several  times  as  a  rope  is  wrapped  around  pulleys. 
Hold  one  pencil  stationary,  and  allow  the  other  one  to  move  as  the 
thread  is  pulled. 

The  action  is  similar  to  that  of  the  pulleys,  except  that  the  friction 
is  greater. 

Teach  that  the  weight  to  be  lifted  divided  by  the  number  of  threads 
running  between  the  pencils  equals  the  power  (provided  there  is  no 
friction).  This  is  the  “law”  of  the  pulleys. 

Notice  that  the  hand  representing  the  power  moves  as  many  times 
as  far  as  the  load  moves  as  there  are  cords  between  the  pulleys. 

Thus  the  gain  in  power  is  just  equal  to  the  loss  in  speed.  This  is 
true  in  all  machines. 

The  Cog  Wheels. — An  egg  beater  or  an  old  clock  will  serve  to 
illustrate  the  cog  wheels. 

Show  that  cog  wheels  may  he  used  to  gain  either  speed  or  power, 
depending  on  the  relative  sizes  of  the  wheels. 

The  number  of  cogs  on  the  large  wheel  divided  by  the  number  on 
the  small  wheel  equals  the  gain  of  power  or  speed  as  the  case  may 
be.  This  is  the  “law”  of  the  cog  wheels. 

Belt  and  Belt  Wheels. — The  most  convenient  form  of  apparatus 
for  demonstration  will  probably  be  the  bicycle,  in  which  the  chain 
is  a  sort  of  belt  and  the  sprockets  are  the  belt  wheels. 

The  law  is  that  the  speed  gained  is  got  by  dividing  the  size  of 
one  wheel  into  the  size  of  the  other.  In  the  case  of  the  bicycle,  the 
number  of  teeth  on  the  sprockets  may  be  taken  as  the  sizes  of  the 
wheels. 

The  Inclined  Plane. — This  requires  merely  a  short  board,  one 
end  of  which  may  be  raised  by  laying  it  on  a  pile  of  books.  Roll  or 
slide  some  object  up  the  board,  pointing  out  the  fact  that  the  weight 
to  be  lifted  is  as  many  times  the  force  required  as  the  length  of  the 
board  is  times  the  height  of  the  incline.  This  is  the  “law”  of  the 
inclined  plane. 

Give  some  problems,  such  as  the  force  required  to  roll  a  200-pound 
barrel  up  a  board  twelve  feet  long  into  a  wagon  three  feet  high. 

Reciuire  diagrammatic  drawings. 

Explain  that  a  1  per  cent  or  a  5  per  cent  grade  means  a  grade  rising 
1  foot  or  5  feet  to  the  hundred. 


SAN  DIEGO  state  NORMAE  SCHOOE. 


23 


The  Screw. — As  good  an  example  as  any  of  the  screw  is  the  vise. 

Let  the  distance  between  the  threads  be  measured,  and  also  the 
distance  that  the  hand  moves  in  turning  the  lever. 

The  latter  divided  by  the  former  will  give  the  number  of  times 
the  force  is  multiplied  by  the  use  of  the  instrument.  (“Law”  of  screw.) 

Discuss  the  resistance  to  be  overcome  and  the  approximate  gain  in 
power  in  the  case  of  the  ordinary  screw,  the  jack  screw,  etc. 

The  Windlass. — A  spool  revolving  on  a  nail  driven  into  a  board 
with  a  strip  of  wood  a  few  inches  long  tacked  to  one  end  of  the  spool 
for  a  crank  will  illustrate  this  machine. 

Show  how  easy  it  is  to  lift  a  weight  by  means  of  it. 

Give  the  rule  for  finding  the  power  gained.  The  power  gained  is 
equal  to  the  diameter  of  the  axle  divided  into  double  the  length  of 
the  crank.  (“Law”  of  windlass.) 


24 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


LIGHT. 


The  Sources  of  Light. — Begin  the  topic  of  light  with  a  conversa¬ 
tional  lesson  on  the  sources  of  light.  Let  the  pupils  suggest  the 
sources  and  discuss  each. 

(o)  The  sun,  the  principal  source. 

(b)  The  stars.  These  are  suns  like  our  sun  but  so  far  away  that 
they  seem  dim. 

(c)  The  moon-reflected  sunlight. 

(d)  Fire  of  all  kinds  including  gas  light  and  lamp  light. 

(e)  Red  hot  or  white  hot  substances.  This  includes  electric  lights, 
both  the  arc  light  and  the  incandescent  (bulb)  light. 

All  bodies  begin  to  glow  with  a  red  heat  at  525°  F. 

(f)  Phosphorescence.  Instruct  the  pupils  to  wet  a  match  and  rub 
it  gently  on  something  in  the  dark  and  to  report  results. 

(g)  So-called  “phosphorescence”  of  certain  forms  of  animal  life. 
The  firefly  is  a  notable  example.  The  light  of  the  firefly  is  made  at 
will  and  without  apparent  heat.  The  phenomenon  known  as  phos¬ 
phorescence  in  the  ocean  which  produces  a  flash  of  brilliance  at  each 
dip  of  the  oar  and  causes  fish  to  leave  a  bright  trail  behind  them  as 
they  dart  through  the  water,  is  the  result  of  millions  of  microscopic 
living  organisms  called  noctiliica.  These  become  abundant  only  at 
certain  times  of  the  year. 

Speed. — Awaken  curiosity  among  the  children  to  know  whether 
light  requires  any  time  in  which  to  travel. 

Would  a  light  made  at  a  distance  be  instantly  seen? 

If  a  window  shade  several  miles  away  were  suddenly  drawn  at 
night,  would  the  light  within  reach  a  watcher  instantly, — that  is,  would 
you  see  the  light  as  soon  as  the  curtain  was  drawn? 

It  has  been  found  by  experiments  somewhat  similar  to  the  above 
that  light  takes  time  to  travel  any  distance,  but  that  it  goes  with  such 
great  velocity  that,  could  it  go  in  a  circle,  it  would  travel  seven  times 
around  the  earth  in  a  second. 

How  fast  does  sound  travel? 

Why  do  we  see  the  flash  of  a  gun  before  we  hear  the  report? 

Reflection. — What  is  echo?  What  is  reflection? 

Use  a  mirror  to  reflect  sunlight,  showing  that  in  order  to  throw 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


25 


the  light  back  toward  the  sun,  the  light  must  fall  perpendicularly  upon 
the  glass. 

Turn  the  mirror  so  as  to  cast  the  reflection  to  one  side  and  show 

that  the  angle  or  slant  at  which  the  light  strikes  the  mirror  is  equal 

to  the  angle  or  slant  at  which  it  leaves  the  mirror. 

Prove  the  same  fact  by  holding  the  mirror  so  that  it  will  face  the 
class  and  letting  them  see  that  those  directly  in  front  of  it  can  see 
their  own  reflection  in  it.  Those  on  one  side  can  see  those  on  the 
other. 

Represent  these  facts  in  a  diagram. 

A  rubber  ball  will  obey  the  same  law  in  rebounding.  Try  the 

experiment. 

The  force  of  gravity  prevents  the  hall  from  perfectly  obeying  this 
law. 

Does  gravity  affect  light?  Why  not?  (Light  is  not  a  substance.) 

Reflectors.  Mention  as  many  things  as  you  can  that  are  good 

reflectors. 

Almost  any  surface  will  reflect  if  smooth  enough.  For  example, 
polished  metal,  a  varnished  table  top,  cloth  worn  smooth,  an  unrufiied 
pond. 

Diffusion. — Light  coming  from  a  rough  object  is  said  to  be  dif¬ 
fused,  not  reflected.  The  rough  surface  scatters  the  light  in  all  direc¬ 
tions  because  the  rays  strike  the  particles  composing  the  surface  at 
all  angles.  As  they  are  not  thrown  off  at  any  one  angle,  no  image  is 
formed.  If  the  surface  of  glass  is  roughened  by  grinding,  light  does 
not  shine  straight  through  it  but  is  diffused  in  all  directions  so  that 
we  cannot  see  any  objects  through  it. 

Define  the  words  translucent  and  transparent.  Almost  as  much  light 
shines  through  translucent  glass  as  through  that  which  is  transparent. 

Refraction  (bending). — Show  by  putting  a  pencil  into  a  cup  of 
water  that  it  seems  to  be  bent. 

Teach  that  it  is  the  light,  not  the  pencil,  that  is  bent. 

Light  is  always  bent  when  passing  through  a  surface  except  when 
it  passes  through  perpendicularly. 

The  bottom  of  a  cup  seems  to  be  raised  by  pouring  in  water. 

A  pencil  held  behind  a  thick  piece  of  glass  seems  to  be  set  off 
to  one  side  of  its  true  place  when  viewed  at  an  angle. 

Indians  learn  to  throw  the  spear  in  spear-fishing  lower  down  than 
the  apparent  place  of  the  fish. 


26 


PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCHOOL. 


.When  light  is  bent  (refracted),  it  is  also  separated  into  colors,  but 
this  separation  is  often  so  slight  as  not  to  be  noticeable. 

If  a  prism  can  be  secured,  illustrate  with  it  both  bending  and  separa¬ 
tion  into  colors. 

Color. — Make  and  study  as  varied  a  collection  as  possible  of 
colors  and  shades  of  color. 

Discuss  differences  of  similar  tints. 

Hold  a  prism  in  the  sunlight  so  that  the  spectrum  formed  will  fall 
upon  the  ceiling  or  wall. 

The  prism  separates  the  light  into  these  colors. 

Teach  that  light  is  made  up  of  all  the  colors.  When  mixed  as  they 
are  in  sunlight  we  see  none  of  them.  But  the  prism  separates  them 
and  puts  them  side  by  side.  These  colors  are  called  the  spectrum. 

How  many  separate  colors  can  you  see  in  the  spectrum,  or  in  the 
rainbow,  which  is  a  spectrum  made  by  drops  of  water  in  the  air? 

We  see  any  colored  object  by  means  of  that  color  which  it  reflects 
to  us. 

White  reflects  all  the  colors  and  black  none  of  them.  Black,  then, 
is  the  absence  of  color.  An  object  reflects  no  light  if  perfectly  black. 

To  illustrate  the  last  statement,  make  with  an  eraser  or  moist  cloth 
a  clean  spot  on  the  blackboard.  The  rest  of  the  board  in  contrast 
to  this  spot  looks  far  from  black.  It  reflects  some  light.  The  spot 
will  appear,  especially  to  one  with  half-closed  eyes,  like  the  entrance 
to  a  dark  cave.  It  reflects  practically  no  light. 

Images. — If  light  from  an  object  passes  through  a  lens  or  through 
a  small  hole,  an  image  will  be  formed. 

Make  a  hole  as  large  as  a  pencil  through  a  piece  of  cardboard. 
Darken  the  room  as  well  as  possible,  and  hold  the  cardboard  between 
a  lighted  candle  and  a  piece  of  white  paper,  each  a  few  inches  from 
the  card.  An  image  will  be  seen  on  the  paper. 

If  a  lens  can  be  had,  substitute  it  for  the  perforated  card;  and  if  the 
distance  be  varied  suitably,  an  image  much  clearer  than  that  of  the 
first  experiment  is  secured. 

In  this  way  is  an  image  formed  in  the  camera.  In  taking  a  photo¬ 
graph  this  image  is  made  permanent. 


SAN  DIEGO  STATE  NORMAE  SCHOOL. 


27 


SOUND. 


See  Higgins,  “First  Science  Book,”  p.  91,  or  any  text-book  on  Physics. 

Vibrations. — Strike  a  bell  and  gently  touch  the  edge  with  the 
finger-tips  to  feel  the  vibrations. 

If  a  tuning-fork  is  at  hand,  it  may  be  used  in  the  same  way,  and  also 


Fig.  5. — A  convenient  and  effective 
sonometer.  Wire  stretched  across  a  door, 
which  acts  as  a  sounding  board. 


may  be  plunged  into  a  glass  of  water  while  sounding  to  make  the  vibra¬ 
tions  visible. 

Stretch  a  string  or  wire  and  pluck  it,  so  that  the  vibrations  may  be 
both  seen  and  heard. 

This  may  be  done  very  satisfactorily  by  fastening  one  end  of  a  wire. 


28 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


such  as  is  used  on  brooms,  to  the  hinge  of  a  door,  passing  the  other 
end  around  the  door  knob  and  drawing  it  tight  with  the  hand.  .When 
the  wire  is  made  to  vibrate,  its  tone  is  greatly  reinforced  by  the  door, 
which  acts  as  a  sounding-board. 

Vibrate  a  yard  stick,  pointer,  or  some  such  article,  by  laying  it  on  a 
table  and  holding  it  firmly  with  one  end  projecting  far  enough  to  make 
a  good  tone. 

Using  a  stringed  instrument  of  any  kind,  show  that  as  long  as  the 
tone  continues  the  strings  are  vibrating. 


Fig.  6. — Experiments  in  the  transmission  of  sonncl.  A  pasteboard  megaphone,  a  garden 
hose  speaking  tube,  a  long  pole  to  show  that  solids  carry  faint  sounds  better  than  air  does, 
a  rope  to  show  waves. 


The  sound  made  by  a  humming-bird  is  caused  by  the  vibration  of  its 
wings. 

There  must  be  at  least  sixteen  vibrations  per  second  to  produce  sound. 

How  Sound  Travels. —  Hold  a  yardstick  or  long  pole  with  one 
end  to  a  child’s  ear.  Scratch  the  other  end  slightly.  Take  it  away  from 
the  ear  and  make  the  same  noise.  Sound  does  not  travel  so  well  in 
air  as  in  wood. 

Sound  travels  in  waves  through  air  or  other  substance. 

Discuss  water  waves.  Does  the  water  move  forward  as  far  as  the 
wave  goes? 


SAN  DIEGO  STATE  NORMAE  SCHOOL. 


29 


Lay  a  long  rope  on  the  floor  or  ground.  Fasten  one  end  of  it,  and 
taking  the  other  end  in  the  hand,  send  a  wave  along  it  while  it  touches 
the  floor.  Notice  that  the  tighter  the  rope  is  stretched  the  faster  the 
wave  travels.  The  stretching  makes  the  rope  more  elastic ;  that  is,  it 
flies  back  into  position  more  ciuickly  after  being  bent. 

Sound  travels  fifteen  times  as  fast  in  an  iron  railroad  track  as  in  air 
because  the  iron  is  more  elastic  than  air. 

Does  the  fact  shown  above  that  sound  travels  with  more  force  in 
wood  than  in  air  prove  that  it  also  goes  faster  in  the  wood? 


Fig.  7. — \"elocity  of  sound.  A  ten-inch  pendulum  vibrating  half  seconds  measures  the  time 
necessary  for  the  return  of  an  echo  of  a  sound  made  by  clapping  two  boards  together. 


The  String  Telephone  (see  Higgins  “First  Science  Book,”  p.  96.) 
Connect  two  tin  cans  by  means  of  a  strong  string  about  100  feet  long. 
Stretch  the  string  tightly  and  talk  into  one  can  while  some  one  listens 
at  the  other.  If  the  string  is  run  out  through  an  open  window,  one 
person  may  talk  into  the  outer  can,  while  all  in  the  room  may  hear  the 
sound  as  it  comes  from  the  can  within.  Take  care  that  the  string 
touches  nothing  and  is  tightly  stretched. 

Sound  waves  pass  along  the  string.  This  is  in  no  way  similar  to 
an  ordinary  telephone,  for  there  no  sound  goes  over  the  wire,  but  an 
electric  current  which  reproduces  the  sound  at  the  other  end. 


30 


PHYSICAL  nature:  STUDY,  ELEMENTARY  SCHOOL. 


The  Speaking  Tube. — Let  one  pupil  talk  into  one  end  of  a  long 
garden  hose,  the  other  end  being  brought  around  the  corner  of  the 
house  or  through  a  window.  All  near  this  end  can  hear  the  words  as 
they  come  from  the  tube. 

In  this  case  the  sound  v/aves  are  not  allowed  to  spread  in  all 
directions,  but  are  confined  to  the  air  within  the  tube. 

The  Megaphone. — Make  a  megaphone  of  pasteboard.  Let  one 
pupil  speak  through  it  from  a  distance.  The  megaphone  directs  the- 
sound  forward  in  one  direction. 

Speed  of  Sound. — With  the  class  out  of  doors  find  how  far  sound 
will  travel  in  a  second. 

Make  a  pendulum  which  will  vibrate  half  seconds  by  tying  a  stone  to- 
a  string  ten  inches  long.  Send  a  pupil  walking  away  from  the  class  with 
two  boards  to  clap  together.  Let  him  stop  from  time  to  time  and  clap 
the  boards.  Release  the  pendulum  as  the  boards  are  seen  to  strike. 
Let  the  boy  go  on  until  it  requires  the  time  of  two  swings  of  the  pendu¬ 
lum  for  the  sound  to  reach  the  class. 

Later  have  two  pupils  measure  this  distance  and  report  to  the  class.. 
It  should  be  about  1100  feet. 

Interest  the  pupils  in  finding  the  velocity  of  sound  by  timing  sounds 
at  great  distances,  such  as  steam  whistles  or  the  firing  of  guns  or 
cannon.  A  watch  with  a  second  hand  should  be  used.  The  time 
elapsing  between  seeing  the  steam  from  the  whistle  and  hearing  the 
sound  gives  the  distance.  Each  second  represents  1100  feet,  or  five 
seconds  a  mile. 

J^clocify  in  Iron.  If  a  car  track  having  the  rails  exposed  down  to- 
the  ties  is  within  reach,  take  the  class  to  it,  and  by  striking  the  rail  two 
or  three  hundred  feet  distant  from  your  pupils,  you  will  produce  two 
successive  sounds,  one  coming  through  the  rail  and  the  other  through 
the  air.  ( If  earth  is  filled  in  against  the  rails,  the  vibrations  are  dead¬ 
ened  and  sound  will  not  travel.) 

The  distance  to  a  flash  of  lightning  can  be  found  by  counting  the 
seconds  between  the  flash  and  the  thunder  clap  and  multiplying  this  by 
five,  since  sound  travels  about  one  fifth  of  a  mile  11100  feet)  per  second. 

Echo. — Take  the  class  to  a  point  opposite  a  flat  wall,  such  as  the 
side  of  a  house.  Make  sharp  sounds — for  example,  by  clapping  two 
boards  together. 

Find  how  close  to  the  wall  the  sounds  may  be  made  and  yet  give  an 
echo.  If  too  close,  the  echo  and  the  original  sound  are  so  nearly 
simultaneous  that  they  appear  as  one. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


31 


Why  do  large  rooms  echo  more  than  small  ones  ?  ( Sound  and  echo 

are  not  simultaneous.) 

Why  is  a  flat  wall  l^etter  than  an  irregular  one? 

Why  do  we  need  to  be  directly  opposite  the  wall? 

Make  the  sound  at  an  angle  from  the  wall  and  see  where  the  pupils- 
must  be  to  hear  the  echo. 

Stand  between  two  houses  and  notice  a  doul)le  echo. 

Go  into  an  unfurnished  room  and  listen  to  the  many  confused  echoes. 

Reverberation  of  thunder  in  the  mountains  is  caused  by  the  sound 
re-echoing  back  and  forth  from  mountain  sides. 

Why  does  furniture  in  a  room  help  to  prevent  echo?  (The  sound 
waves  are  broken  up  as  water  waves  are  by  rocks  projecting  from  the 
surface.) 


32 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL- 


MAGNETISM. 


To  perform  experiments  a  magnet,  costing  a1)ont  20  cents  at  a 
hardware  store,  is  necessary. 

What  a  Magnet  will  Attract.  Show  that  nothing  but  iron  and  steel 
are  attracted.  Try  many  metals  and  use  the  occasion  to  call  attention 
to  the  metals,  their  names  and  uses. 


Fic.  8. — A  home-made  electromagnet  lift¬ 
ing  shingle  nails.  (A  few  cents  worth  of 
small  magnet  wire  wrapped  on  a  bolt  or 
large  nail.) 


Test  pins,  needles,  pens,  wire,  etc.,  to  see  if  made  of  iron  or  steel. 
Making  Magnets.  Any  piece  of  hard  steel,  as  a  knife  blade,  a  needle, 
or  a  pen,  may  be  magnetized  by  rubbing  it  on  a  magnet. 


SAN  DIEGO  STATE  NORMAE  SCHOOE. 


33 


Rub  one  end  of  a  needle  on  one  pole  of  the  magnet,  then  turn  it 
about  and  rub  the  other  end  on  the  other  pole  of  the  magnet. 

Magnetize  a  number  of  needles  thus  and  float  them  on  a  large  pan 
of  water  on  thin  disks  of  cork. 

If  the  points  of  all  the  needles  have  been  rubbed  on  the  south 
pole  of  the  magnet,  they  will  be  north  poles  and  will  point  north,  act¬ 
ing  as  compass  needles. 

Action  of  Poles  Upon  Each  Other  Show  that  when  the  points  (north 
poles)  are  brought  near  to  each  other  in  the  water,  they  repel  each 
other. 

Show  that  the  same  is  true  of  the  eye  ends. 

But  when  a  north  and  a  south  pole  are  brought  near  to  each  other, 
they  draw  together  and  hold. 

Bring  successively  the  north  and  south  poles  of  the  magnet  near  to 
the  ends  of  the  needles.  Predict  in  each  case  what  the  result  will  be. 

Summarize  the  facts  illustrated  above  as  follows :  Like  poles  repel 
each  other  and  unlike  poles  attract. 

Break  a  needle  in  two  and  show  that  it  is  now  two  magnets  with  a 
pole  at  each  end.  This  would  be  the  case  were  the  needle  broken 
into  any  number  of  pieces. 

Show  by  lifting  small  articles,  such  as  tacks  or  iron  filings,  that 
the  greatest  strength  of  the  magnets  is  near  the  end  (at  the  poles). 

Put  the  magnet  on  a  table  and  lay  over  it  a  piece  of  white  paper.. 
Sprinkle  iron  filings  on  this  to  show  the  “lines  of  force”  which  sur¬ 
round  a  magnet. 

It  will  be  seen  that  the  force  is  not  in  the  magnet  alone  but  around  it. 

If  one  end  of  a  nail  is  held  very  near  to  the  pole  of  a  magnet,, 
it  becomes  for  the  time  a  magnet  and  will  pick  up  bits  of  iron.  When 
the  magnet  is  removed,  the  nail  loses  its  power. 

Electromagnets.  Wrap  a  fine  insulated  wire  a  hundred  times  or 
more  about  a  large  nail  or  bolt.  Pass  a  current  from  a  battery  of  sev¬ 
eral  cells  through  the  wire  and  the  nail  will  become  a  magnet.  It  loses 
most  of  its  magnetism  when  the^  current  is  stopped. 

This  principle  is  used  in  the  electric  bell  and  many  other  electrical 
instruments,  as  explained  below  where  these  instruments  are  described- 


.34 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


ELECTRICITY. 


Material  Required:  An  electric  bell,  45  cents;  10  cents  worth  of  small 
(No.  25)  magnet  wire;  a  dry  cell,  30  cents  (or  a  number  of  worn-out 
dry  cells  which  can  be  revived  as  indicated  below). 

This  newest  and  most  important  science  should  form  a  part  of  a 
nature  study  course  because  of  the  interest  which  children,  especially 
boys,  take  in  the  subject.  Many  of  the  applications  of  electricity,  such 
as  lighting,  heating,  and  bell-ringing,  are  as  intimately  concerned  in  the 
life  of  the  girl  as  of  the  boy,  and  being  a  matter  of  daily  observation, 
deserve  a  place  in  the  nature  study  course. 

In  order  to  make  any  study  of  electricity  profitable,  some  electrical 
apparatus  is  essential.  As  nearly  every  school  has  one  or  more  boys, 
even  as  early  as  the  fifth  school  year,  who  are  interested  in  electricity 
and  have  made  and  collected  electrical  material  of  various  sorts,  all 
that  is  needed  can  often  be  secured  through  the  pupils. 

The  first  necessity  will  be  a  few  battery  cells  and  a  little  wire. 
Worn-out  batteries  may  be  secured  in  abundance  from  a  garage.  These 
may  be  put  into  fairly  good  working  order  by  punching  a  number  of 
Roles  in  the  zinc  coating  and  setting  them  in  cans  of  water.  The  cans 
must  not  touch.  They  often  work  well  enough  without  any  treatment. 

Insulated  wire  is  inexpensive  and  should  be  used,  but  ordinary  broom 
or  clothes  line  wires  will  serve  the  purpose,  if  not  allowed  to  touch 
each  other. 

A  study  of  the  cell  itself  is  the  first  thing  to  undertake. 

The  “dry  cell”  consists  of  a  zinc  plate  (the  container  itself),  and  a 
carbon  plate  (the  rod  in  the  center),  and  a  moist  substance  packed 
in  between  the  plates. 

Take  a  dry  cell  apart. 

Most  cells  contain  a  liquid  instead  of  the  moist  solid  of  the  “dry 
cell.” 

All  cells  are  essentially  the  same,  having  two  plates  of  different 
material  and  a  liquid  between. 

Let  pupils  find  out  all  they  can  of  materials  used  in  different  bat¬ 
teries  and  report  in  class. 

In  almost  all  cells  one  plate  is  zinc.  The  second  plate  is  usually 
either  carbon  or  copper. 

The  liquid  used  may  be  salammoniac,  or  sulphuric  acid,  or  chromic 
acid.  Other  chemicals  are  used  in  some  cells. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


35 


Any, two  metals  in  almost  any  solution  would  give  some  current. 

Several  cells  connected  form  a  battery. 

There  are  two  ways  of  connecting  cells,  in  “series”  and  in  “parallel.” 

If  all  the  zinc  plates  are  connected  and  all  the  carbon  plates  are  con¬ 
nected,  the  connection  is  in  “parallel.” 

But  if  the  zinc  of  each  is  connected  with  the  carbon  of  the  next  cell, 
the  result  is  connection  in  “series.” 

Series  connection  is  usually  best. 

If  a  bell  can  be  secured,  ring  it  with  one  cell,  then  connect  several 
cells,  and  notice  difference  in  the  loudness  of  the  ring. 

A  bell  on  the  wall  may  be  connected  with  a  battery  on  the  floor. 
The  bell  is  so  typical  of  many  electrical  instruments  that  one  should 
be  purchased  if  possible  for  the  use  of  the  school.  The  cost  is  50 
cents  or  75  cents. 


Fig.  9. — The  electric  bell,  showing  the  essential  parts  and  the  course  of  the 
electric  current. 

The  Bell. — Before  making  an  explanation  of  the  bell,  refer  to 
the  experiment  above  in  which  a  current  in  a  coil  of  wire  wrapped 
around  a  bar  of  iron,  such  as  a  nail  or  bolt,  will  make  a  magnet  of  the 
har.  While  the  current  is  flowing,  the  bar  will  pick  up  iron  filings  or 
tacks,  and  attract  knife  blades  or  other  small  pieces  of  iron. 

Start  and  stop  the  current  several  times,  noticing  that  the  bar 
loses  its  magnetism  when  the  current  is  broken. 

The  electric  bell  has  an  iron  bar  wrapped  with  wire,  and  when  the 
current  is  started  this  becomes  a  magnet  and  draws  the  iron  tapper 
against  the  bell.  When  the  tapper  moves,  however,  it  makes  a  gap 
which  breaks  the  current,  and  the  iron  ceases  to  be  a  magnet  and  the 
tapper  springs  back  into  place.  The  gap  is  now  closed,  the  current 
starts  again,  and  another  tap  is  given.  This  process  repeated  makes  the 
tapper  sound  continuously. 


36 


PHYSICAI,  NATURE  STUDY,  EEEMENTARY  SCHODE. 


The  bell’s  action  may  be  more  easily  imderstood  if  it  is  analyzed  into 
successive  steps  as  follows  : 

( 1 )  The  current  flows  from  the  battery  to  the  thumbscrew  or  “bind¬ 
ing  post”  A,  Fig.  9  and  around  the  iron  spools,  making  the  iron  into 
a  magnet. 

(2)  This  magnet  instantly  draws  the  iron  “keeper”  to  itself,  making 
the  tapper  which  is  fastened  to  the  “keeper”  strike  the  bell. 

(3)  As  the  keeper  is  drawn  to  the  magnet,  it  leaves  a  gap  between 
itself  and  the  metal  point  C,  thus  stopping  the  current. 

(4)  The  current  being  stopped,  the  magnetism  is  destroyed  and  the 
keeper  is  thrown  by  the  spring  back  against  C,  thus  allowing  the  current 
to  start  again. 

(5)  The  whole  process  is  now  repeated,  causing  another  tap.  Con¬ 
stant  repetitions  cause  the  bell  to  ring  continuously. 

The  Push  Button. — This  is  a  means  of  closing  a  gap  in  the  wire 
circuit,  thus  allowing  a  current  to  flow. 


c  Fig.  10. — Telegraph  apparatus  made  at  an  expense  of  ten  cents.  Two  houses  may  be 
put  into  telegraphic  communication  by  means  of  fence  wire. 


The  Telegraph. — A  very  good  telegraph  sounder  may  be  made  by 
any  boy  at  an  expense  of  five  or  ten  cents  for  insulated  wore. 

A  small  bolt  is  wrapped  with  several  hundred  turns  of  fine  (No.  25) 
magnet  wire,  and  the  end  of  the  bolt  is  put  into  a  close-fitting  hole  bored 
in  a  board  as  shown  in  Fig.  10.  An  upright  board  is  nailed  on  back  of 
this  bolt,  making  a  convenient  place  to  attach  a  tapper  which  consists 
of  a  large  nail.  This  is  supported  at  one  end  on  a  small  nail,  b,  and  at 
the  other  by  a  rubber  band  hung  from  a  nail  r,  so  that  the  tapper  and 
the  nail  are  about  one  thirty-second  of  an  inch  apart.  A  small  nail  d 
serves  to  make  the  tap  double,  as  it  should  be. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


37 


A  “key”  to  use  with  this  sounder  is  made  as  follows : 

Into  a  board  three  or  four  inches  square  drive  a  small  nail  at  in,  Fig, 
10,  to  which  a  long  nail  mn  is  fastened  with  a  wire.  This  nail  is  held 
up  (so  that  one  end  is  about  a  quarter  of  an  inch  above  the  board) 
by  means  of  a  twisted  rubber  band  stretched  between  the  nails  o  and  p. 
It  is  pressed  down  with  the  finger  until  it  touches  the  nail  head  r  to- 
which  the  battery  wire  is  attached,  thus  making  connection  so  that  the 
sounder  clicks. 

One  or  two  good  dry  cells  or  three  or  four  old  cells  soaked  up  in 
cans  of  water  will  operate  the  instrument  well. 

The  key  and  battery  can  be  placed  on  one  side  of  the  room  and  the. 
sounder  on  the  other,  or  in  another  room  ;  they  can  be  connected  with 
any  sort  of  wire,  (not  necessarily  insulated).  Pupils  can  connect  two 
houses  a  short  distance  apart  in  this  way  provided  the  wires  do  not 
touch  the  ground. 


Fig.  10a. — Telegraphic  instruments  shown 
by  diagram  in  Fig.  10.  A  good  piece  of 
manual  training  work  for  boys. 


The  key  in  a  sender’s  office  is  similar  to  the  push  button  used  for 
door  bells.  It  closes  a  gap  and  allows  the  electricity  to  fiow. 

Each  tap  of  the  operator  sends  a  current  to  the  sounder  in  a  distant 
city.  The  sounder  is  similar  to  a  bell.  Each  time  a  current  is  sent 
into  it,  it  becomes  a  magnet  and  draws  the  tapper  down.  A  bell  serves 
excellently  as  a  sounder  if  used  as  described  below. 

Connect  the  bell  at  one  end  of  the  room  with  a  battery  of  two  or 
three  cells  at  the  other  end.  The  connection  is  made  by  means  of  two- 
wires.  Have  a  gap  in  one  of  the  wires  near  the  battery  which  can  be 
closed  by  touching  the  cut  ends  to  serve  as  a  sending  key. 

The  bell  may  be  made  to  tap  like  a  telegraph  sounder  by  connect- 


38 


PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCHOOL. 


ing  the  screw  “C”  back  of  the  tapper  with  a  binding  post  “B”  by 
means  of  a  short  wire.  See  Fig.  9. 

The  Electric  Light. — Show  the  class  an  incandescent  electric 
bulb.  Note  how  the  two  ends  of  a  carbon  fibre  are  fastened  to  two 
wires  which  are  sealed  into  the  glass.  The  current  goes  in  on  one  of 
these  wires,  passes  through  the  carbon  fibre,  heating  it  red  hot,  and 
passes  out  OYer  the  other  wire. 

If  air  could  get  into  the  bulb,  what  would  happen  to  the  carbon? 

If  yon  hace  a  burned-out  bulb,  break  it  to  show  the  effect  of  letting 
air  suddenly  into  a  vacuum. 

Since  the  invention  of  the  tungsten  filament,  to  be  used  instead  of 
carbon,  a  great  saving  in  electricity  can  be  made  by  its  use.  Tungsten 
is  a  metal  which  is  capable  of  giving  more  than  twice  as  much  light  as 
carbon,  using  the  same  amount  of  electricity. 

Arc  lights  used  for  street  lighting  have  two  carbon  rods  held  about 
a  quarter  of  an  inch  apart  so  that  the  current  must  jump  across  the  gap. 
In  doing  so  it  heats  the  ends  of  the  rods  to  about  3800  degrees,  the 
highest  temperature  known  on  earth.  (The  sun’s  temperature  is  thought 
to  be  about  twice  that.) 

Frictional  Electricity. — Small  amounts  of  electricity  may  be  gen¬ 
erated  by  rubbing  together  certain  substances. 

To  be  successful  with  these  experiments,  you  must  have  very  dry 
Aveather.  A  “desert  day”  is  best. 

Rub  a  stick  of  sealing  wax  or  a  fountain  pen  (hard  rubber)  with  a 
woolen  cloth;  or  rub  a  piece  of  glass  (a  lamp  chimney)  with  a  silk 
cloth  (silk  coat  lining).  A  genuine  rubber  comb  run  through  the  hair 
several  times  will  serve  the  purpose. 

Fine  bits  of  tissue  paper  will  be  picked  up  by  either  the  sealing  wax, 
glass,  or  rubber  comb. 

It  is  this  sort  of  electricity  that  the  frictional  machines  generate  for 
X-ray  work. 

Discussion  of  Other  Applications. — Although  it  is  impossible  in 
the  elementary  schools  to  perform  elaborate  experiments  in  electricity, 
it  is  desirable  that  every  child  whether  he  is  to  go  into  science  in  the 
high  school  or  is  to  leave  school,  should  leave  the  grades  with  some 
definite  idea  of  the  uses  of  electricity  which  are  so  intimately  connected 
with  the  life  both  of  the  boy  and  the  girl. 

There  are  often  boys  in  the  class  who  have  gained  a  large  amount 
of  information  from  their  practical  experiments  and  observations,  and 
may  be  interested  and  stimulated  by  a  discussion  which  goes  farther 


SAN  DIEGO  state  NORMAE  SCHOOL. 


39 


than  is  within  the  province  of  the  school  to  demonstrate  with  experi¬ 
ments. 

If  it  is  possible  to  arrange  with  the  manager  of  a  garage  or  power 
house  to  have  the  children  taken  where  electrical  apparatus  can  be 
shown  them  and  explained  by  those  in  charge,  it  will  be  very  instructive 
and  interesting. 

A  talk  by  a  practical  electrician  after  the  class  has  been  given  the 
principles  of  the  subject  will  carry  them  farther  than  it  would  be 
possible  for  the  teacher  to  do. 

Following  are  some  of  the  subjects  which  might  well  be  discussed 
and  perhaps  illustrated  by  pictures  or  excursions  to  shops. 

(1)  The  electromagnet  used  for  lifting  heavy  iron.  This  is  a  magnet 
similar  to  that  found  in  the  bell  except  that  it  is  very  large  and  is 
fastened  to  a  crane.  It  is  employed  in  foundries  and  in  loading  cars. 
The  end  of  the  magnet  is  brought  against  an  iron  boiler  or  keg  of  nails, 
for  example,  the  current  is  turned  on,  when  instantly  the  iron  adheres 
to  the  magnet  and  can  be  lifted  by  the  crane.  When  it  is  desired  to 
let  go,  the  current  is  turned  off.  The  magnet  is  sometimes  used  for  a 
broom  to  sweep  up  scrap  iron  on  the  floor  of  a  foundry. 

(2)  Electric  Heaters.  In  these  the  principle  is  similar  to  that  of  the 
incandescent  bulb,  that  is,  the  wire  through  which  the  current  is  made 
to  pass  in  the  instrument  becomes  very  hot.  Examples  are  the  electric 
toaster  and  the  electric  flat  iron.  If  these  can  be  brought  (by  a  pupil, 
perhaps)  and  shown  the  class  they  will  be  better  understood. 

The  most  significant  thing  about  such  heaters  is  that  the  wire  in 
the  heater  becomes  hot  and  that  in  the  cord  leading  to  it  there  is  no 
heat.  The  reason  is  that  the  heat  is  developed  only  where  there  is 
great  resistance,  and  the  wire  used  is  of  different  material  from  that 
used  in  the  cord  and  offers  more  resistance  to  the  flow  of  the  current. 

About  eight  or  ten  times  as  much  electric  current  is  used  in  a  toaster 
or  flat  iron  as  in  a  sixteen-candle  power  light. 

(3)  Electric  Motors  and  Dynamos.  A  dynamo  is  an  instrument 
which  if  turned  will  generate  a  current. 

A  motor  is  an  instrument  which  will  turn  (and  will  make  other 
machinery  turn )  if  a  current  is  run  into  it.  The  details  of  construction 
must  be  left  for  the  high  school. 

Let  pupils  give  uses  of  a  motor, — for  example,  to  run  a  street  car, 
an  electric  automobile,  a  sewing  machine,  many  kinds  of  farm  machines, 
(such  as  a  cream  separator,  an  irrigation  pump,)  the  suction  pump  in 
a  vacuum  cleaner,  the  electric  fan,  and  a  great  variety  of  saws,  lathes, 
€tc.,  in  a  machine  shop. 


40  PHYSICAI.  NATURE  STUDY,  ELEMENTARY  SCHOOL. 

(4)  Spark  Coils  for  Automobiles  and  Other  Gasoline  Motors.  Alt 
gasoline  motors  are  run  by  the  force  of  successive  explosions  of  gas 
which  take  place  in  the  cylinder.  Each  explosion  is  caused  by  an 
electric  spark  igniting  the  gas.  A  battery  is  not  strong  enough  tO' 
give  such  a  spark,  and  so  a  spark  coil  is  used.  This  is  made  of  a 
double  spool  of  wire,  one  spool  slipped  inside  another.  The  outer 
spool  has  one  hundred  or  more  times  as  much  wire  as  the  inner  spool,, 
sometimes  several  miles  of  it.  The  current  from  a  battery  of  several 
cells  is  run  into  the  inner  coil.  This  generates  a  current  in  the  outer- 
coil  which  has  more  force  than  the  battery  current  has  and  is  capable 
of  giving  sparks. 

(5)  Bleetro plating.  Plated  silver  ware  is  made  by  immersing  ware- 
made  of  some  cheaper  metal  in  a  bath  containing  a  silver  solution.  A 
bar  of  silver  is  placed  in  the  bath  near  the  things  to  be  plated,  and 
then  a  current  is  passed  from  the  bar  to  the  metal  ware,  through  the 
solution.  The  current  dissolves  away  the  silver  of  the  bar  and  carries 
it  through  the  solution  and  deposits  it  evenly  all  over  the  spoon  or 
whatever  the  ware  may  be. 

(6)  The  Transformer.  Why  are  men  working  on  light  and  power 
lines  sometimes  killed  by  touching  a  wire,  while  accidents  seldom  occur 
in  houses  lighted  by  electricity  which  comes  from  these  lines?  Within 
a  few  hundred  feet  of  every  house  where  current  is  used  may  be  seen, 
a  black  iron  box  on  top  of  a  pole,  from  which  the  wires  come  supply¬ 
ing  the  houses  near  by.  These  boxes  are  transformers.  They  reduce- 
the  force  of  the  current  so  that  it  is  safe  to  use.  The  amount  of 
current  is  not  decreased  to  any  extent  by  the  transformer,  but  its 
foree  is  lessened.  It  would  not  do  to  transform  it  at  the  power  house 
for  the  whole  city  at  once,  because  it  needs  its  force  to  carry  it  for 
long  distances  through  the  wires. 

The  spark  coil  used  in  automobiles  is  a  kind  of  transformer ;  but 
instead  of  making  the  force  less,  the  spark  coil  makes  it  greater. 

(7)  Wireless  Telegraphy.  A  wireless  telegraphic  apparatus  consists 
of  a  sender  which  is  a  very  powerful  spark  coil,  and  a  receiver  which 
is  an  aerial  wire  to  which  is  attached  an  instrument  so  delicate  that  it 
will  respond  to  a  very  little  electricity. 

The  spark  coil  sends  out  waves  of  electricity  in  all  directions  like 
the  waves  of  sound  sent  out  all  ways  by  a  person’s  voice.  The  waves 
of  sound  can  be  caught  by  a  person  in  any  direction — similarly  the 
waves  of  electricity  can  be  caught  by  any  one  who  has  a  receiver. 

Just  as  an  ear  trumpet  catches  more  of  the  sound  than  the  ear  alone, 
being  bigger,  so  the  aerial  catches  more  of  the  electric  wave  than  the 
little  instrument  in  the  receiving  office  could  do  alone. 


SAN  DIEGO  state  NORMAL  SCHOOL. 


41 


ASTRONOMY. 


Astronomy  may  seem  at  first  thought  too  difficult  a  science  from 
'which  to  draw  material  to  be  used  in  nature  study.  Very  naturally  a 
teacher  untrained  in  astronomy  will  feel  that  a  suliject  so  vast  and 
intricate  is  more  fitted  for  the  college  student  than  the  elementary 
pupil.  But  this  science  which  has  been  studied  from  the  infancy  of 
the  race  is  full  of  inspiration  and  stimulus  for  the  infant  mind  today. 


Fig.  11. — The  planets.  In  (a)  is  shown  their  orbits  and  their  relative  distances  from 
the  sun.  In  (b)  relative  sizes. 


The  only  ecjuipment  the  teacher  needs  is  to  become  herself  interested 
in  astronomy  and  to  have  sufficient  guidance  in  the  selection  of 
material  suitable  for  children. 

The  following  suggestions  are  made  to  supply  the  latter  need. 

The  Solar  System. — The  first  step  to  take  in  order  to  lead  the 
child’s  mind  out  beyond  the  earth  is  to  give  him  an  idea  of  the  solar 
system.  Illustrations  are  needful  to  this  end ;  verljal  description  will 
not  suffice. 


42  PHYSICAI,  NATURE  STUDY,  EEEMENTARY  SCHOOE- 

The  simplest  illustration  is  the  blackboard  drawing.  A  series  oi 
concentric  circles  representing  the  orbits  of  the  planets  about  the  suit 
should  be  placed  by  the  pupils  in  notebooks  kept  for  such  diagrams, 
and  for  notes. 

No  diagram  of  the  sort  can  l)e  made  to  represent  correctly  all  the 
relationships  of  size  and  distance.  Like  a  raised  map,  it  is  intended 
to  be  suggestive  rather  than  accurate  as  to  scale. 

By  means  of  a  number  of  diagrams  each  intended  to  present  one 
fact,  it  is  quite  possible  to  work  to  scale  and  thus  give  correct  propor¬ 
tions. 

For  example,  the  relative  distance  of  the  planets  from  the  sun 
should  be  shown  thus  : 

Place  at  one  end  of  the  blackboard  a  dot  for  the  sun.  A  dot  5 
inches  from  this  will  represent  Mercury.  Venus  is  shown  by  a  dot 
in.  from  the  sun,  the  earth,  12  in..  Mars,  1  ft.  2  in.,  the  asteroids,  2- 
ft.  9  in.,  Jupiter,  5  ft.,  Saturn,  9  ft.  6  in.,  Uranus,  19  ft.,  Neptune,  30  ft.. 

By  curved  lines  show  portions  of  the  orbits  ;  the  time  of  one  revolu¬ 
tion  about  the  sun  (one  year  of  the  planet)  may  be  written  on  each.. 
See  Fig.  11. 

Another  set  of  relationships  among  the  planets  is  that  of  size. 

Let  a  permanent  illustration  of  this  be  made  by  cutting  from  paper  a. 
set  of  circles,  the  diameters  of  which  represent  respectively  the  diam¬ 
eters  of  the  planets.  These  may  be  pasted  on  the  blackboard  in  the 
order  of  the  planet’s  distance  from  the  sun,  thus  serving  to  teach  both 
size  and  order  of  the  planets. 

Convenient  sizes  for  these  circles  are  as  follows :  Mercury,  Fs  inch ; 
Venus,  1  inch;  earth,  1  inch;  Mars,  Jd  inch;  Jupiter,  11  inches;  Saturn,. 
9  inches;  Uranus,  4  inches;  Neptune,  4  inches. 

The  height  of  some  object  in  the  room,  as  for  example,  the  door  and 
its  transom,  may  be  selected  to  represent  the  diameter  of  the  nine-foot 
circle  requisite  to  show  the  size  of  the  sun  upon  the  same  scale. 

An  easily  made  model  which  makes  the  relative  positions  and  motions 
of  the  solar  system  objective  is  shown  in  Fig.  12. 

The  sun  is  represented  by  a  ball  S,  suspended  by  a  string  as  shown, 
and  anchored  to  the  floor  so  that  it  will  be  stationary.  H  is  a  smaller 
ball  representing  the  earth.  P  represents  any  other  planet,  and  M  the 
moon.  The  whole  being  attached  to  the  ceiling  by  means  of  the  cord  cd,. 
is  made  to  revolve  about  the  center  S.  The  moon  makes  several  revolu¬ 
tions  about  E  while  E  passes  once  about  S — several  months  to  each  year. 

Rotation  of  the  planets  and  the  sun  is  also  seen. 


SAN  DIEGO  state  NORMAL  SCHOOL. 


43 


44 


PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCHOOL. 


P  may  be  made  to  revolve  in  a  smaller  circle  than  B,  representing 
Mercury  or  Venus,  or  in  a  large  circle,  representing  one  of  the  outer 
planets. 

The  Sun. — After  a  clear  conception  of  the  solar  system  as  a 
whole  has  been  gained,  some  time  should  be  given  to  the  consideration 
of  each  member  of  the  system,  especially  of  the  sun. 

When  we  have  learned  the  sun’s  distance  from  us,  93,000,000  miles, 
its  size  can  be  determined  easily  by  the  pupils  in  the  following  manner : 

Darken  the  room  as  thoroughly  as  possible.  Draw  down  the  shades. 
Make  a  pinhole  in  one  shade  so  that  the  sun  can  shine  through  on  to 
the  floor,  or,  better,  on  a  piece  of  white  paper  held  4  or  5  feet  from 
the  pinhole.  The  circular  spot  of  light  is  the  image  of  the  sun. 

The  diameter  of  this  image  divided  into  its  distance  from  the  hole  in 
the  shade  is  equal  to  the  diameter  of  the  sun  divided  into  its  diameter. 
Thus  using  the  distance  of  the  sun,  93,000,000  miles,  it  is  easy  to  find 
that  the  diameter  of  the  sun  is  about  866,000  miles.  See  Fig.  13. 


Fig.  13. — Mea.suring  the  size  of  the  sun.  The  diameter  of  the  spot  a  is  to  the  distance  b 
as  the  sun’s  diameter  is  to  93,000,000. 


Such  images  of  the  sun  are  a  familiar  sight  upon  the  ground  in  a 
forest.  The  openings  among  the  leaves  correspond  to  the  pinhole  of 
our  experiment. 

Another  observation  to  be  made  upon  the  sun  is  for  the  purpose  of 
finding  its  apparent  motion  north  and  south  throughout  the  seasons. 

Measure  the  length  of  the  noon  time  shadow  of  a  house  or  other 
object  from  week  to  week  and  note  the  changes  in  length.  This  is  a 
simple  method  of  testing  the  seasonal  motion. 

A  more  instructive  method  may  be  shown  by  means  of  apparatus 
made  as  follows :  Into  a  board  about  a  foot  square  drive  a  nail  near 
one  corner.  See  Fig.  14.  Describe  a  circle  about  the  nail  as  a  center 
and  divide  the  circle  into  degrees.  The  shadow  of  the  nail  at  noon 
falls  across  the  circle  at  a  certain  point  depending  upon  the  position 
of  the  sun.  The  figure  at  this  point  gives  the  distance  of  the  sun 
;south  of  us. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


4S 


The  distance  from  our  zenith  to  the  equator  is  given  by  our  latitude. 
Thus  the  distance  of  the  sun  north  or  south  of  the  ecjuator  is  easily 
found. 

In  the  diagram  (Fig.  14)  the  shadow  at  56°  shows  that  the  sun  is. 
56°  south  of  the  observer’s  zenith.  Suppose  the  observer  to  be  in 
latitude  32l4°,  then  the  sun  must  be  233/2°  south  of  the  equator,. 
— 56°  minus  32^^°. 

This  will  be  the  condition  on  the  22d  of  December. 


c^uns  La^itudi- 

TT 


Fig.  14. — A  “sun  board.”  The  reading  at  noon  shows  how  many  degrees  the  sun  is'- 
to  the  south  of  us.  Daily  readings  show  sun’s  apparent  motion  north  or  south. 


In  this  manner  the  class  can  find  the  position  of  the  sun  on  any 
day  in  the  year. 

Especial  observation  should  be  made  of  the  equinoxes  and  solstices. 
The  cause  of  this  apparent  motion  of  the  sun  can  be  shown  by  a 
simple  demonstration. 


46 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL- 


Use  a  sphere  to  represent  the  earth  (a  small  globe  will  do  or  an 
apple  with  a  pencil  circle  to  mark  the  equator).  Let  a  pupil  stand  to 
represent  the  sun.  Pass  the  sphere  around  the  child,  keeping  the  axis 
tilted  23k^°  (approximately)  from  the  perpendicular  and  pointed 
always  in  the  same  direction.  It  will  be  seen  that  in  one  portion  of 


Fig.  14a. — “Sun  board”  shown  by  diagram  in  Fig.  14. 

the  circle  the  child  is  looking  (the  sun  is  shining)  directly  upon  the 
eciuator ;  in  another  portion  he  is  looking  upon  the  part  above  the 
equator ;  and  in  a  third  upon  the  part  below  the  equator. 

Day  and  Night. — Using  a  globe,  a  series  of  demonstrations  may 
be  made  which  cannot  fail  to  be  helpful  in  giving  the  pupil  a  clear 
conception  of  the  varying  length  of  the  day  throughout  the  year  in 
various  latitudes.  See  Fig.  15. 


SAN  DIEGO  state  NORMAE  SCHOOE. 


47 


Set  the  globe  in  the  sunshine  so  that  the  light  covers  it  from  pole 
to  pole.  It  is  now  falling  perpendicularly  upon  the  equator,  as  may 
be  shown  by  standing  a  pencil  or  other  object  on  the  equator  vertically 
with  respect  to  the  globe.  It  casts  no  shadow.  This  is  the  condition 
September  23d  and  March  21st. 

Now  place  two  chalk  spots  upon  the  glo])e  in  different  latitudes  but 
upon  the  same  meridian.  They  represent  two  persons.  Turn  the 
globe  and  they  will  be  seen  to  enter  the  shadow  simultaneously  and 
emerge  simultaneously.  This  shovv^s  that  with  the  sun  over  the  equator 
the  days  are  of  equal  length  in  all  latitudes.  The  nights  also  are  of 
equal  length. 

Moreover,  it  will  be  seen  that  the  path  traversed  by  each  of  these 
points  crosses  twelve  hour  circles  in  the  light  portion  and  the  same  in 
the  dark.  The  days  are  equal  to  the  nights.  This  is  the  season  of  the 
equinox. 

To  show  why  winter  days  are  short  in  northern  latitudes,  tilt  the 
globe  so  that  the  sunshine  falls  23l4°  short  of  the  north  pole.  Show 
as  before  that  the  sun  is  now  vertical  at  the  tropic  of  Capricorn.  This 
represents  December  22d.  Leave  the  chalk  spots  placed  as  they  were 
before.  Now  turn  the  globe,  and  the  more  northern  one  is  seen  to 
enter  the  shadow  sooner  than  the  one  farther  south.  Sunset  in  that 
latitude  comes  earlier;  the  day  is  shorter.  To  determine  by  how  much 
the  day  is  shorter,  count  the  hour  spaces  as  before. 

By  similar  demonstration  the  northern  summer  days  can  be  shown 
to  be  long.  The  globe  should  now  stand  so  that  the  sun  shines  23^4 ° 
past  the  north  pole.  See  Fig.  15. 

To  show  the  reason  for  continuous  day  or  night  at  certain  seasons 
in  the  Arctic  Circle  :  Place  a  chalk  spot  near  the  pole.  On  rotation  of 
the  globe  while  in  the  summer  position,  the  spot  does  not  enter  the 
shadow  at  all.  During  rotation  of  the  globe  while  in  the  winter 
position,  the  spot  remains  constantly  in  the  shadow. 

The  length  of  day  in  the  year  in  the  observer’s  latitude  (or  elsewhere) 
may  easily  be  found  as  follows : 

By  reference  to  the  analemma,  printed  on  most  globes,  ascertain  the 
distance  of  the  sun  north  or  south  of  the  equator  upon  that  day.  (Or, 
this  information  may  be  determined  by  the  pupils,  using  the  “sun 
board,”  Fig.  14.)  Having  obtained  the  position  of  the  sun,  set  the 
globe  so  that  the  sun’s  rays  shall  fall  vertically  in  that  latitude  and 
then  proceed  as  above  to  find  the  length  of  day  and  night  in  the  ob¬ 
server’s  latitude. 


48 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL. 


Difference  of  Temperature  in  Different  Zones. — That  the  torrid 
zone  is  hot  because  of  its  vertical  sun  has  but  little  educational  sig¬ 
nificance,  unless  we  teach  why  it  is  that  vertical  rays  are  hotter  than 
those  which  are  slanting  as  in  the  frigid  zones. 

The  false  impression  prevails  that  vertical  rays  beat  down  with  more 
force,  or  that  the  slanting  rays  glance  off. 


A  simple  diagram  will  make  the  matter  clear. 


cl  a  14  5 

Fig.  15. — Diagram  of  a  globe  standing  in  the  sunshine.  A  method  of  showing  the 
effect  of  latitude  and  season  upon  relative  length  of  day  and  night. 

In  Fig.  16  let  Sah  and  Scd  be  two  cones  of  rays  of  equal  size  and 
therefore  of  equal  amounts  of  heat  from  the  sun.  The  slanting  cone 
Sah  is  distributed  over  more  surface,  as  shown  by  the  diagram,  than 
the  vertical  cone  Scd,  and  therefore  the  heat  in  any  point  in  ah  is  less 
intense  than  in  cd. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


49 


IS 


Fig.  16. — Showing  why  perpendicular  rays  are  hotter 
than  slanting  rays. 

The  Planets. —  Little  special  information  about  individual  planets 
need  be  given,  but  the  thought  of  their  similarity  to  the  earth  should 
be  made  distinct.  They  should  be  studied  rather  as  constituting  the 
solar  system  than  as  individual  objects  of  interest. 

Observation. — Encourage  evening  study  of  the  “wandering  stars,”  as 
the  ancients  called  the  planets.  Find  from  an  almanac  those  visible ; 


1 

4 

4 

Jt 

¥ 

4 

^  'Ys/jus 

Fig.  17. — Fixed  stars  and  a  moving  planet.  Let  pupils  make 
two  such  drawings  from  nature,  with  an  interval  of  several  weeks 
between. 


make  a  sketch  showing  position  with  reference  to  several  conspicuous 
stars  near  by.  A  few  weeks  later  compare  the  planets’  positions  with 
those  shown  by  the  diagram. 

For  example  suppose  Venus,  which  is  often  visible  as  the  brightest 
object  in  the  western  sky,  is  seen  to  be  in  a  position  such  as  is  repre¬ 
sented  in  “A,”  Fig.  17.  Some  days  or  weeks  later  it  will  have  mov^ed 
and  may  occupy  a  position  relative  to  the  stars,  like  that  shown  in 
“B.”  The  stars,  however,  will  be  seen  to  be  tixed  with  reference  to  one 
another. 


50 


PHYSICAIv  NATURE  STUDY,  EEEMENTARY  SCHOOL- 


Discuss  the  cause  of  this  motion  amouo-  the  stars. 

It  takes  Jupiter,  the  outermost  planet  which  is  plainly  visible,  twelve 
years  to  pass  once  around  the  sun.  How  many  degrees  does  it  move 
annually  among  the  stars? 

The  Moon. — Refer  to  Fig.  11  for  the  position  and  motion  of  the 
moon  relative  to  the  other  members  of  the  solar  system. 

This  diagram  shows  only  the  motion  of  the  moon  with  reference  tO' 
the  earth. 

It  also  moves  with  the  earth  about  the  sun  once  a  year,  making  about 
twelve  revolutions  around  the  earth  while  the  earth  and  moon  are  going 
once  around  the  sun  (twelve  months  in  the  year). 

Use  the  model  of  the  solar  system,  Fig.  12,  to  show  this  double 
motion. 

The  monthly  revolution  of  the  moon  about  the  earth  may  be  observed. 
It  produces  the  eastward  motion  of  the  moon  among  the  stars. 

Establish  first  by  observation  that  all  of  the  heavenly  bodies  appear 
to  move  once  about  the  earth  each  day  from  east  to  west,  making  sun, 
moon,  and  stars  rise  in  the  east  and  set  in  the  west  every  24  hours. 
But  impress  upon  the  pupils  the  fact  that  this  motion  is  only  apparent,, 
and  is  caused  by  the  earth’s  rotation  on  its  axis. 

Teach  the  fact  that  the  eastward  motion  of  the  moon  among  the 
stars  is  a  real  motion  of  about  30°  a  day. 


The  Moon’s  Phases. 

Have  pupils  draw  a  “progressive  diagram”  which  shall  resemble  Fig. 
18  when  finished. 

To  explain  the  cause  of  change  of  phase  is  simple,  if,  indeed,  necessary 
after  such  a  drawing  has  been  completed. 

The  educational  value  of  a  drawing  made  from  nature  is  greater  than 
that  of  a  copy  made  from  a  book. 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


51 


Find  from  a  calendar  when  a  new  moon  may  be  expected,  and  upon 
that  evening  at  sunset  draw  the  moon  showing  its  shape  and  position 
relative  to  the  sun  as  seen  in  Fig.  18. 

On  successive  days  for  two  weeks  add  to  this  drawing  the  new  form 
and  position  of  the  moon  at  sunset. 

Why  does  the  full  moon  always  rise  at  sunset? 

Mark  the  age  of  the  moon  in  each  case. 

The  eastward  motion  of  the  moon  about  the  earth  once  in  four  weeks 
should  be  discussed. 


Fig.  19. — Kodak  picture  of  the  moon  and  Venus.  Ten  exposures  of 
five  seconds  each  at  intervals  of  about  two  minutes;  then  a  twenty-minute 
exposure,  followed  by  four  exposures  at  five-minute  intervals. 


Additional  concreteness  may  be  given  this  subject,  however,  by  paint¬ 
ing  a  ball  half  white  and  half  black  to  represent  light  and  darkness  on 
the  surface  of  the  moon.  Then,  holding  the  ball  in  various  positions 
before  the  class,  let  them  see  the  crescent,  the  half  circle,  the  full  circle, 
and  other  intermediate  forms  which  are  assumed  by  the  illuminated 
portion  of  the  moon  as  it  goes  through  its  various  phases. 

Eclipses  of  Sun  and  Moon. — The  cause  of  eclipses  can  be  made 
clear  by  means  of  a  diagram.  See  Fig.  20. 


.52 


PHYSICAL  NATURE  STUDY,  ELEMENTAKY  SCHOOL. 


When  the  moon  is  between  earth  and  sun,  as  at  (Fig.  20)  its 
shadow  falls  on  a  small  part  of  the  earth  and  the  sun’s  light  is  eclipsed 
for  the  people  living  within  the  region  of  the  shadow. 

When  the  moon  is  beyond  the  earth  from  the  sun,  as  at  it  passes 
through  the  earth’s  shadow  and  is  eclipsed  for  all  the  people  on  that 
side  of  the  earth. 

The  moon  would  be  eclipsed  once  a  month  but  that  it  usually  passes 
in  front  of  or  behind  the  shadow,  not  through  it. 

Solar  and  lunar  eclipses  are  about  equally  frequent. 

Why  is  a  solar  eclipse  so  rare?  A  glance  at  Fig.  20  will  show  that 
shadow  causing  the  solar  eclipse  falls  on  a  very  small  portion  of  the 
earth’s  surface  and  is  therefore  visible  to  but  few  people,  whereas  the 
people  on  half  of  the  earth’s  surface  see  every  eclipse  of  the  moon. 

Comparison  of  the  Moon  With  the  Earth. — A  consideration  of 
some  of  the  differences  between  the  moon  and  the  earth  will  help  us  to 
appreciate  certain  laws  of  nature  as  we  see  them  upon  earth. 

The  moon  being  smaller  than  the  earth,  the  force  of  gravity  there  is 
one  ninth  what  it  is  here. 

How  much  would  an  average  man  weigh  if  on  the  moon? 

If  he  can  jump  two  feet  high  here,  how  high  could  he  jump  there? 

Steeper  mountain  slopes  can  stand  on  the  moon  than  would  be  pos¬ 
sible  here  where  the  weight  of  the  rocks  tears  them  loose,  thus  helping 
to  level  our  mountains.  The  lunar  mountains  are  steep  and  rugged. 

The  moon  is  uninhabitable  by  lieings  like  ourselves  for  lack  of  air 
and  water,  these  vapors  having  Hown  away  from  it  by  reason  of  their 
lightness.  The  earth  holds  its  air  by  force  of  gravity. 

As  the  moon  has  no  clouds  or  water  vapor  or  air,  the  sun  beats 
fiercely  upon  its  barren  surface,  heating  it  intensely.  The  heat  escapes 
at  night,  for  it  is  not  retained  by  a  blanket  of  air ;  and  the  lunar  night 
is  probably  colder  than  any  portion  of  the  earth  in  winter. 

The  moon  rotates  upon  its  axis  once  in  about  thirty  days ;  thus  its  day 
.and  night  are  each  of  two  weeks’  duration. 

How  would  such  days  inconvenience  us? 


/ 


SAN  DIEGO  STATE  NORMAL  SCHOOL. 


53 


des.— Our  tides  are  .produced  chiefly  by  the  moon.  It 
vco  great  tidal  waves  which  sweep  around  .the  world  bringing 
to  every  coast  twice  a  day.  Many  things,  such  as  continents 
^shallow  water,  inter Tere  with  these  waves;  the  sun  also  has  an 

fpon  the  tides.  But  the  action  of  these  minor  forces  may  be 

in  a  class  discussion  of  tides. 

represents  the  action  of  the  moon  upon  the  waters  surround- 
'’earrn.  r/ic  citti-Hctive  force  of  the  moon  upon  the  water  at  a 
greater  than  the  force  wtth  it  the  earth,  because  the 

water  is  nearer  to  the  moon  than  is  the  earth.  The  water  at  c,  however, 
is  drawn  with  less  force  by  the  moon  than  is  tlie  earth  ;  therefore,  the 
earth  is  drawn  away  from  the  water  which  is  left  heaped,  as  at  a.  At 

h  and  d  the  water  flows  away  to  supply  the  tidal  waves  a  and  c;  thus 

low  tide  occurs  at  h  and  d. 


Lour 


Lour 

Fig.  21. — The  cavise  of  tides.  The  clear  space  represents  the  water  of  the  oceans 
encircling  the  earth,  a.  h,  c,  and  d  are  successive  positions  which  an  island  or 
continent  occupies  as  it  is  carried  around  by  the  earth’s  daily  rotation,  passing, 
at  intervals  of  six  hours,  through  regions  of  high  and  low  tide. 


We  may  think  of  the  moon  as  passing  around  the  earth  once  a  day 
(as  it  seems  to  do  and  the  tides  following  it,  or  we  may  think  of  the 
moon  as  standing  almost  still,  as  it  really  does,  holding  the  tides  sta¬ 
tionary  below  it,  while  the  earth  turns  giving  to  any  particular  place  on 
its  surface  high  and  low  tides  alternately. 

Thus,  in  Fig.  21,  if  a  certain  island  or  continent  is  at  a,  it  is  in  a 
region  of  high  tide,  but  six  hours  later  when  the  earth  b}^  its  rotation 
has  carried  it  round  to  b,  it  is  in  the  region  of  low  tide.  Six  hours 
later  it  passes  through  high  tide  (c),  and  six  hours  thereafter  it  is  at 
d  (low  tide),  and  comes  around  to  the  original  high  tide  after  the  lapse 
of  about  a  day. 


PHYSICAL  NATURE  STUDY,  ELEMENTARY  SCHOOL 


Fig.  22. — Star  trails  in  the  north  polar  regions.  Such^a  picture,  though  fainter, 
can  be  made  with  a  kodak.  This  picture  was  made  with  an  improvised  camera 
consisting  of  a  stereopticon  lens  mounted  in  one  side  of  a  small  goods  box  having 
a  hole  cut  in  the  opposite  side  for  a  plate-holder.  The  time  of  exposure  was  two 
and  one  half  hours. 

Such  a  picture,  made  by  teacher  or  pupils,  is  a  very  instructive  demonstration  of 
the  apparent  motion  of  the  heavens — the  real  motion  of  the  earth.  Notice  that  the 
“north  star”  (the  very  bright  one)  is  some  distance  (1)4°)  from  the  true  pole. 


SAN  DIEGO  STATE  NORMAE  SCHOOE. 


55 


Jrs. — That  stars  are  suns — apparently  small  and  dim  be- 
[heir  great  distance — is  the  first  lesson  for  pupils  to  learn, 
what  a  sun  is.  It  is  large,  intensely  hot,  gives  light  of 
^  the  center  around  which  revolve  planets  such  as  our 

^tars  have  their  systems  of  planets,  possibly  inhabited ; 
[being  so  far  away  and  having  no  light  of  their  own, 
viSTOie  TO'  us.  j 

^n  illustration  of  the  T’^ance  to  the  stars  will  heln  to  make  the 
facts  above  comprehensible. 

If  we  use  the  blackboard  diagram  mentioned  in  the  discussion  of 
the  solar  system  in  which  one  foot  is  taken  as  the  distance  of  the  sun 
to  the  earth  and  thirty  feet  as  the  distance  to  Neptune  (the  outermost 
planet  of  the  solar  system),  . the  distance  to  the  nearest  star  will  be  fifty 
miles.  The  North  Star  on  the  same  scale  would  be  500  miles  from 
the  earth. 

These  vast  distances  account  for  the  fact  that  the  stars  do  not  seem 
to  move  about  among  themselves.  Their  only  apparent  motion  is  that 
caused  by  the  rotation  of  the  earth  which  makes  them  rise  and  set. 
Unlike  the  planets  the  stars  are  “fixed.”  An  illustration  will  make  the 
cause  of  this  evident. 

When  ships  are  seen  far  out  at  sea  or  animals  are  observed  at  a 
distance  of  several  miles,  it  is  impossible  unless  we  watch  for  some  time 
to  tell  if  they  are  moving. 

A  life  time  is  not  long  enough  to  ascertain  if  the  stars  move. 
Astronomers  have  means  of  finding  that  they  are  in  rapid  motion  in 
all  directions ;  but  the  relative  position  of  stars  to  one  another  in  the 
constellations  has  been  what  it  is  now  for  thousands  of  years. 


The  Constellations. — The  names  of  some  of  the  more  distinct 
constellations  should  be  learned  and  the  pupils  taught  to  recognize  them. 
A  few  evening  sessions  of  the  class  are  advisable. 

Young’s  Uranography,  a  booklet  priced  at  30  cents  and  published  by 
Ginn  &  Co.,  gives  good  maps  of  the  constellations  and  some  account 
of  each  as  well  as  of  the  principal  stars  of  the  constellations. 

The  following  constellations  are  easily  identified : 

The  Big  Dipper  (Ursa  Major),  Cassiopeia,  Orion  (after  November), 
Canis  Major,  Canis  Minor,  The  Sickle,  and  the  Pleiades  during  the 
spring. 

A  fine  set  of  maps,  one  for  each  month,  can  be  secured  by  subscribing 
for  the  Monthly  Evening  Sky  Map,  published  at  Columbia  University 


56  PHYSICAL  NATURE  STUDY,  EEEMENTARY  SCH^ 

for  $n00.  This  four-page  pubncation  contains  a  good  deaf 
tion  aside  from  the  maps.  The  stars,  being  in  the  same  posf 
cessive  years,  a  set  of  these  maps  would  become  a  perm 
atlas. 

The  following  books  are  sufficiently  popular  in  sbdm 
to  the  teacher  who  wishes  to  become  informed  upc 
astronomy.  They  are  standard  works  and  easily  fouij 

Star  Land,  (Ball),  Ginn  &  Co.  _ _ ^ 

Giant  Sun  and  His  Family,  (Proctor),  Silver,  ffurdette  Co.  — 

Other  Worlds,  (Servibs),  Appleton  _  1  20 

Lesson  in  Astronomy,  (Young),  Ginn  &  Co.  - 1  25 

Elements  of  Astronomy,  (Ball),  MacMillan  _  80 

Nexe  Astronomy,  (Todd),  American  Book  Co.  _  1  30 


The  first  three  books  mentioned  are  easily  within  the  comprehension 
of  grammar  grade  children,  and  are  interestingly  written. 

If  the  course  has  given  the  class  a  desire  to  read  such  books  as  the 
above  and  to  continue  the  observations  which  have  been  begun  in 
school,  it  will  have  accomplished  its  end — to  bring  the  child  into 
intelligent  sympathy  with  nature. 


